Chapter XXXV: Introduction: Division I. Ecardines--External (1)

CHARACTERS--INTERNAL CHARACTERS--DIVISION II.
TESTICARDINES--EXTERNAL CHARACTERS--INTERNAL
CHARACTERS--SYNOPSIS OF FAMILIES--STRATIGRAPHICAL
DISTRIBUTION--PHYLOGENY AND ONTOGENY

=Introduction=

The wide distribution and vast abundance of the Brachiopoda throughout the whole series of geological formations make this group of especial importance to the student of the past history of the earth; and the zoologist must always regard the fossil forms with peculiar interest, because they not only largely outnumber the living representatives, but comprise numerous extinct genera, and even families, exhibiting types of structure and characters entirely absent in the modern members of the group. It is a most fortunate circumstance that the excellent state of preservation in which we frequently find them, and the immense amount of material at our disposal, enable us to determine with accuracy and certainty the internal characters of the shells in the great majority of cases. But it is only since the beginning of the present century that our knowledge of the anatomy of the soft parts of the living animal has rendered any tracing of homologies possible. In the case of features in fossil extinct types the interpretation must be to some extent doubtful. Barrande, Clarke, Davidson, Hall, King, Oehlert, Waagen, de Verneuil, and a host of other workers have contributed to the information which we now possess; and their works must be consulted for details of the subject.[428]

Since all Brachiopods are inhabitants of the sea, the geologist at once recognises as a marine deposit any bed which contains their remains. Under favourable conditions they swarmed in the seas of Palaeozoic and Mesozoic times. Beds of limestone are frequently almost entirely composed of their shells, as, for instance, some of the Devonian limestones of Bohemia. Often they give the facies to the fauna and outnumber in species and individuals all the other organisms of the period. The Ungulite Sandstone (Cambrian) of Russia and the Productus Limestone of the Salt Range in India of Carboniferous and Permian age are well-known examples.

Many species seem to have been gregarious in habit; thus _Productus giganteus_ of the Carboniferous Limestone may generally be found in crowded masses, as in some localities in Yorkshire.

The fact that certain species of Brachiopods characterise definite stratigraphical horizons or “zones” gives them occasionally an importance equal to that of Graptolites; for instance, the Ecardinate species _Trematis corona_ marks a set of beds in the Ordovician, and the isolated _Stringocephalus Burtini_ is restricted to the upper part of the Middle Devonian, giving to the limestone on that horizon its distinctive name. It is noteworthy also how certain species affect a sandy and others a calcareous sea-bottom, so that beds of the same age show differences in their Brachiopod fauna owing to a dissimilar lithological composition.

While few of the recent Brachiopods reach a large size, some of the extinct species measure several inches in breadth, but the great _Productus giganteus_ attained the width of even a foot.

The bright colours of the shells of the living animals are not generally preserved amongst the fossil species from the older rocks; yet in a Carboniferous _Terebratula_ we can even now detect the purple bands in some specimens, and a Cretaceous _Rhynchonella_ similarly exhibits its original colour.

The Brachiopoda are evidently a group in its decline, as the geological record shows; but they date back from the earliest known fossiliferous rocks, in which the Ecardinate division is alone represented. As we ascend through the stratigraphical series the number and variety of genera and species belonging to both divisions rapidly increase until in the united Ordovician and Silurian there are nearly 2000 species and about 70 genera. From this point of maximum development down to the present day there is a gradual decrease in numbers.

According to Davidson, at least 17 Upper Tertiary species are still living on our sea-bottoms; and many recent Mediterranean forms occur in the Pliocene rocks of the islands and shores of that sea, and in the Crags of East Anglia.

A brief review of the chief characteristics of fossil Brachiopoda is given below. Those genera which have the greatest zoological or geological importance can alone be noticed owing to the exigencies of space.

I. ECARDINES

=External Characters=

A considerable diversity of external form is met with even in this division, from the limpet-like _Discina_ to the flattened tongue-shaped _Lingula_. The valves have most commonly a smooth external surface with delicate growth-lines; but sometimes pittings (_Trematis_) or radiating ribs (_Crania_) are present, and in a few forms the shell is furnished with spines (_Siphonotreta_), which perhaps serve to anchor it in the soft mud of the sea-bottom. The usual mode of fixation was by means of the pedicle (= peduncle or stalk), which either (1) passed out simply between the posterior gaping portion of the valves (_Lingula_), or (2) lay in a slit in the ventral valve (_Lingulella_), or (3) pierced the substance of the latter valve by a definite foramen (_Discina_). The first-mentioned condition of the pedicle seems the most primitive. Rarely the pedicle was absent, and the shell was attached by the whole surface of the ventral valve (_Crania_, p. 467).

The two valves in the fossil Ecardines were held together by muscular action, though in some families (_Trimerellidae_) we see traces of articulating processes. The “hinge line,” or line along which the valves worked as on a hinge, is in most forms more or less curved. A “hinge area” (_i.e._ that portion of the shell generally smoother than other parts of the valves, more or less triangular in form, and lying between the beaks on one or both sides of the hinge line), is usually absent in the Ecardines.

=Internal Characters=

Owing to the rarity of well-preserved interiors of valves in this division, our knowledge of their internal characters is still far from satisfactory. The arrangement of the muscular impressions varies greatly amongst extinct genera, but we are often able to interpret them with a considerable amount of certainty by a study of the scars and the muscles of the well-known recent _Lingula_ (Fig. 322). The extreme specialisation of the muscles in many of the earliest genera (_e.g._ _Lingula_) is remarkable, and points to a long but so far undiscovered ancestry in pre-Cambrian times.[429] In fossil species of _Crania_ and _Lingula_ the muscle-scars correspond closely with those in the living representatives of these genera. In the most highly specialised family of the Ecardines--the _Trimerellidae_--we meet with features of peculiar interest.[430] The muscle-scars in this family (Fig. 323, A, B) are most remarkable for the development of the so-called “crescent,” (_q.r.s._) which skirts the posterior margin of both valves as a sub-cardinal impression. It is believed to be the trace of a strong post-parietal muscular wall, analogous in position to that of _Lingula_. The three pairs of “lateral” muscle-scars in the latter genus seem to be represented by the “terminal” (_s_) and “lateral” (_r_) scars on the crescent of the _Trimerellidae_. A pair of “transverse” scars (_t_) occurs in each valve between the “terminals” and the antero-lateral edge of the “platform” (_j_). “Cardinal” (_v_), “sub-cardinal” (_w_), and “umbo-lateral” (_x_) scars also occur. The median impression which covers the “platform” (_j_) consists of a central, lateral, and usually an anterior pair of scars; and the impressions of the genital organs, according to Davidson and King, lie medianly posterior to the “platform.” The “platform” itself is a more or less conspicuous central calcareous elevated area occurring in each valve, but most developed in the dorsal; in some cases it is double-chambered with tubular cavities (“platform vaults,” Fig. 323, A, B, _k_), in others it is more or less solid. It appears to have originated through a posterior shifting of the central muscular bands, that they might be inserted behind the liver; at the same time a deposition of shelly material, to form fulcra to work the heavy valves, took place at these points. The tunnelling-out of the platform was probably due to the continual pressure of the lobes of the liver. The division of the umbonal cavity into definite chambers in _Monomerella_, and to a less extent in other members of this family, appears, according to Davidson and King, to have been caused by pressure of the ovarian lobes.

In connexion with the foregoing remarks on the development of the “platform,” it may be mentioned that the paths along which the muscle-bands move, as the shell of Brachiopods increases in size, are marked by elongated scars, and often by shelly deposits; and when the members of a muscle-pair come into juxtaposition these shelly deposits (which act as fulcra for the muscles) combine, and by the growth of the shell form a septum, as in the case of the median septum of _Lingulepis_.

The _Obolidae_ show some important features in the internal impressions. _Obolella crassa_ (Hall) may be taken as a well-known type of the family. In this species a pair of small scars, one on each side of the pedicle-groove, lies close under the hinge line in the ventral valve. There is also a well-marked scar for the insertion of the pedicle-muscle at the end of the pedicle-groove. A pair of much elongated lateral impressions extending forward from the “cardinals” may be homologous with the “laterals” of _Lingula_; and the two small central scars between them may be compared with the “centrals” of _Lingula_ which are in a somewhat similar position. In the dorsal valve of _O. crassa_ a pair of “cardinals” is found, and on each side of a low median rounded ridge are two small “central” scars. Indistinct “lateral” scars arise close to or in the central area, and diverge anteriorly.

Sometimes a great concentration of muscle-scars occurs round the foramen in the ventral valve, as in _Siphonotreta_.

As regards the minute structure and composition of the shell in the Ecardines, we find that the _Lingulidae_ and _Discinidae_ have their shell composed of alternating layers of phosphate of lime and a corneous substance; the former layers are pierced by microscopic canals. The _Craniidae_ have calcareous shells traversed by tubules, which divide into many fine branches near the external surface; a thin periostracum covers the exterior. The _Trimerellidae_ have heavy thick calcareous shells, for which they required the previously-described elaborate arrangement of muscles to open and shut them.

II. TESTICARDINES

=External Characters=

It is to this division that the great majority of the Brachiopoda belong; and the diversity of form, of ornamentation, and of internal characters is correspondingly greater than in the Ecardines.

A transversely or longitudinally oval shape of shell is the commonest; but sometimes it is triangular, as in _Rhynchonella_ (Fig. 327), or bilobed, as in _Pygope_ (= _Terebratula diphya_). The ventral valve is usually more convex than the dorsal, and the former may be prolonged into a tube by the accelerated growth and infolding of the anterior and lateral margins, producing a very abnormal form (_Proboscidella_). The external surface of the valves is frequently ornamented with more or less prominent radiating ribs; and fine concentric growth-lines are commonly shown, and may be developed into coarse ridges or wrinkles, particularly in old individuals. The members of the family _Productidae_ are usually furnished with tubular spines, which are sometimes of great length, and served to anchor the free shells in the mud, or were twisted round Crinoid stems and similar objects.

In the ventral valve of many genera there is a median sinus, with a corresponding fold in the dorsal valve, and rarely _vice versâ_; sometimes the fold and sinus are double.

The hinge line is either curved or straight, and the valves are articulated by means of a pair of “hinge-teeth” (Fig. 329, _t_) in the ventral valve, which fit into corresponding sockets in the opposite valve. Some genera have the teeth very rudimentary, or have lost them altogether. The teeth are frequently supported by “dental plates,” and the sockets by “socket plates” (_e.g._ _Conchidium_, Figs. 324, 325). A few genera with a long hinge line have the whole of it denticulated (_Stropheodonta_). In the dorsal valve medianly close under the hinge line is a shelly protuberance--the “cardinal process”--to which the diductor muscles are attached. It is sometimes of great length and forked (_Stringocephalus_, Fig. 326), or tripartite, or even quadripartite; but in _Rhynchonella_ and some other genera it is rudimentary.

A “hinge area” (Fig. 334, _c.a_) is often present on one or both valves, and may be of great size, as in _Clitambonites_, but in _Productus_ it is wholly absent. In those genera that possess it a triangular fissure--the “deltidial fissure”--frequently traverses it on both valves; in the dorsal valve the fissure is merely the space between the dental sockets, and may be occupied by the cardinal- process (Fig. 334, C) or covered by a shelly plate--the “chilidium.” In the ventral valve it gives passage to the pedicle, and may be partly or entirely closed by a similar plate (Fig. 334, _d_) known as the “pseudo-deltidium,” especially large in _Clitambonites_, or remain open (_Orthis_). This pseudo-deltidium is a primitive character, and arises in an early stage of the development as a shell-growth on the dorsal side of the animal, becoming attached to the ventral valve subsequently. The pedicle in many genera passes out through a special foramen in the beak of the ventral valve; and its proximal portion is often embraced by a pair of small plates--the deltidial plates or “deltidium”--which are formed on lateral extensions of the ventral mantle lobe, according to Beecher. These plates lie on each side of the pedicle, or grow round and unite in front of it (_Rhynchonella_, Fig. 327), or constitute merely its anterior border (_Terebratula_, Fig. 328). In some cases this foramen becomes closed in old age.

The dorsal valve in a few cases has its beak perforated by a foramen--the “visceral foramen.” This foramen is in no way connected with the pedicle foramen, but points perhaps to the existence in the early Testicardinate genera of an anal aperture. In _Athyris concentrica_ (Devonian) this foramen is connected internally with a cylindrical tube, which extends longitudinally to about one-third the length of the valve. In _Centronella_ the aperture in the cardinal plate is rounded and complete; and in _Strophomena_ and its allies the opening lies between the cardinal processes. If this feature is correctly interpreted, it suggests a retrogression of the group since Palaeozoic times not only in numbers, but in structure; and other evidence points the same way.

=Internal Characters=

The interior of the shell is sometimes more or less divided up by septa. A median septum occurs in one or both valves of many genera as a low ridge or strongly developed partition (_Waldheimia_, Fig. 329, _ss_; and Stringocephalus, Fig. 326, B, _v.s_). _Conchidium_ (Fig. 325) has its dental plates of great size, and uniting to form a V-shaped chamber or “spondylium,” supported by a median double septum; and by means of these with a pair of septa and the large socket-plates in the dorsal valve the interior of the shell of this genus is divided up into several chambers.

The interiors of several other genera are somewhat similarly divided up.

In the Carboniferous genus _Syringothyris_ two special plates, situated between the dental plates, are rolled into an incomplete tube, so as to enclose probably the anal extremity of the alimentary canal; and in several genera a sub-umbonal “cardinal plate” is present, which is perforated (_Athyris_) or slit in some cases for the passage of the anal tube.

For the support of the fleshy “spiral arms” the calcareous structures forming the “brachial apparatus” are of two main types--(1) the loop type; (2) the spiral-cone type. In the _Strophomenidae_ no special calcareous support seems to have been usually present (Fig. 334), though in some species of _Leptaena_ spirally-grooved elevated areas supported the fleshy arms; in the _Productidae_ it is probable that the ridges enclosing the “reniform impressions” (Fig. 333, _i_) served for a similar purpose.

The _Terebratulidae_ show the “loop type” of brachial apparatus. In _Waldheimia_ (Fig. 329), which may be taken as an example, we notice first in the dorsal valve the “crura” (_cr_), from which arise the two “descending branches” which run forwards and then are bent back to form the “ascending branches” which are united by the “transverse band.” In some genera the “ascending branches” may be reduced to mere points, and the “transverse band” become a median vertical plate; the “crura,” too, may be fused so as to form a “crural band”; and the “descending branches” may be connected by a cross band--the “jugal band.” In _Stringocephalus_ (Fig. 326, _l_, _s.p_) the loop is furnished on its inner edge with radiating processes; and in _Argiope_ the loop is simple, not reflected, and fused with marginal septa; while in the _Thecidiidae_ it is more or less fused with the shell itself, and with the mass of calcareous spicules secreted by the mantle.

The “spiral-cone type” of brachial apparatus is found in the _Spiriferidae_, _Atrypidae_, and _Koninckinidae_, and consists of two spirally-enrolled calcified lamellae, forming two cones with their apices directed laterally (_Spirifera_, Fig. 330), or towards the interior of the dorsal valve (_Atrypa_, Fig. 332), or towards each other (_Glassia_); or forming two flat spirals in the same plane (_Koninckinidae_). A “jugal band” is generally present, but varies much in position, and in some genera has complicated posterior processes.

The _Rhynchonellidae_ have no loop or spiral cones, but merely a pair of short “crura.”

The principal modifications in the attachments of the muscles in the _Testicardines_ are illustrated by _Productus giganteus_ (Fig. 333), _Leptaena rhomboidalis_ (Fig. 334), and _Waldheimia flavescens_ (Fig. 329).

In _Productus_ (Fig. 333) we see in the ventral valve a pair of dendritic occlusor, often called adductor, impressions and a pair of large flabellate divaricator impressions. In the dorsal valve the large “cardinal process” served for the attachment of the divaricator, and a low median septum separated the dendritic occlusor scars, which are rarely divisible into anterior and posterior pairs.

In _Leptaena_ (Fig. 334) the occlusor scars (_a_) in the ventral valve are narrow and median, and are enclosed by a pair of flabelliform divaricator impressions (_d.v_); in the dorsal valve two pairs of occlusor scars (_a.a_, _p.a_) are well marked, and accessory posterior occlusor scars are traceable in some specimens. The vascular sinuses (_v.s_) and genital areas are conspicuous in many species of this and other genera.

In _Waldheimia_ (Fig. 329) a sub-umbonal “peduncular muscle” scar (_p_) in the ventral valve has before it a pair of “accessory divaricator” scars (_a.d_) flanked by a pair of “ventral adjustor” (_v.a_) and a pair of “divaricator” impressions (_d_), between which lie the two occlusor scars (_a_). In the dorsal valve anterior and posterior pairs of occlusor scars (_a.a_, _a.p_) are visible.

The minute structure of the calcareous shell of the Testicardines is of flattened fibrous prisms inclined at a very acute angle to the surfaces. In many forms minute tubes more or less closely arranged pierce through the fibrous shell-substance; but in some genera (_Productus_) they do not reach the outer surface (see p. 468). Allied genera, however, differ much in the punctate or impunctate character of the shell.

SYNOPSIS OF FAMILIES

I. ECARDINES

Family. _Lingulidae_

Shell elongated, composed of alternating chitinous and
calcareous layers, the latter of which are perforated. Attached
by a pedicle passing between apices of valves.

Arms have no calcified supports.

(For muscles see Fig. 322.)

RANGE.--Lower Cambrian to Recent.

PRINCIPAL GENERA.--_Lingula_, _Lingulella_, _Lingulepis_.

Family. _Obolidae_

Shell varies in shape. Ventral valve provided with pedicular
groove or foramen. Cardinal border thickened. No brachial
supports. Shell composed of alternating chitinous and calcareous
layers.

(For muscles see p. 496.)

RANGE.--Lower Cambrian to Devonian.

PRINCIPAL GENERA.--_Obolus_, _Obolella_, _Kutorgina_,
_Linnarssonia_, _Siphonotreta_, _Acrotreta_, _Neobolus_.

Family. _Discinidae_

Shell rounded, valves more or less conical, fixed by pedicle
passing through slit or tubular foramen in ventral valve. No
calcified brachial supports. Shell structure chitino-calcareous.

RANGE.--Ordovician to Recent.

PRINCIPAL GENERA.--_Discina_, _Orbiculoidea_, _Trematis_.

Family. _Craniidae_

Shell calcareous, subcircular; fixed by surface of ventral
valve; dorsal valve the larger, depressed-conical. Shell
structure punctate.

Four principal muscular scars in each valve, with central
triangular protuberance in ventral valve (see p. 476).

RANGE.--Ordovician to Recent.

PRINCIPAL GENUS.--_Crania_.

Family. _Trimerellidae_

Shell thick, calcareous, inequivalve; beak of ventral valve
usually prominent; rudimentary teeth maybe present; hinge area
well developed, with pseudo-deltidium. In interior of valves
muscular platform, “crescent,” and sometimes sub-umbonal
chambers (see p. 494, Fig. 323).

RANGE.--Ordovician and Silurian; maximum in Wenlock.

PRINCIPAL GENERA.--_Trimerella_, _Monomerella_, _Dinobolus_,
_Rhinobolus_.

II. TESTICARDINES

Family. _Productidae_

Shell entirely free, or fixed by ventral valve or spines.
Concavo-convex, more or less covered with tubular spines. Hinge
line straight. Hinge-teeth absent or rudimentary.

Cardinal process prominent.

Reniform impressions in dorsal valve.

(For muscular impressions see p. 501, Fig. 333.)

RANGE.--Silurian to Permian. Genus _Productus_ very
characteristic of the Carboniferous.

PRINCIPAL GENERA.--_Productus_, _Chonetes_, _Strophalosia_,
_Proboscidella_, _Aulosteges_.

Family. _Strophomenidae_

Shell very variable in shape; concavo-convex, plano-convex,
or biconvex; hinge line usually straight; frequently with an
area on each valve; foramen may or may not be present. Shell
structure near always punctate. Ventral valve usually furnished
with hinge-teeth; and dorsal valve with cardinal process.

Brachial supports completely absent or very rudimentary.

(For muscular impressions see p. 502, Fig. 334.)

RANGE.--Wholly Palaeozoic.

PRINCIPAL GENERA.--_Orthis_, with many sub-genera,
_Clitambonites_, _Skenidium_, _Strophomena_, _Orthothetes_,
_Leptaena_, _Stropheodonta_, _Plectambonites_.

Family. _Koninckinidae_

Shell plano-convex or concavo-convex. Brachial apparatus
composed of two lamellae spirally enrolled in the same plane, or
in the form of depressed cones, with the apices directed into
the ventral valve.

RANGE.--Silurian to Lias.

PRINCIPAL GENERA.--_Koninckina_, _Koninckella_, _Coelospira_,
_Davidsonia_.

Family. _Spiriferidae_

Shell biconvex. Brachial apparatus consisting essentially of two
descending calcareous lamellae which by spiral enrolment form a
pair of laterally-directed cones (Fig. 330).

RANGE.--Chiefly Palaeozoic, but a few forms pass up into the
Lias.

PRINCIPAL GENERA.--_Spirifera_, _Cyrtia_, _Uncites_, _Athyris_,
_Merista_.

Family. _Atrypidae_

Brachial apparatus consists of two descending calcareous
lamellae which bend outwards at the extremity of the crura and
are coiled into two spiral cones, the apices of which either
converge towards each other (_Glassia_) or towards the dorsal
valve (_Atrypa_, Fig. 332), or diverge towards the dorsal valve
(_Dayia_); shell structure impunctate.

RANGE.--Ordovician to Trias.

PRINCIPAL GENERA.--_Atrypa_, _Dayia_, _Glassia_.

Family. _Rhynchonellidae_

Shell biconvex, hinge line usually curved.

Beak of ventral valve incurved, with foramen.

Calcareous brachial supports reduced to a pair of short curved
crura.

The septa, dental and socket plates may be highly developed and
divide up the cavity of the shell into chambers (_Stenochisma_,
_Conchidium_).

Shell structure fibrous, rarely punctate; muscular impressions
as in _Terebratulidae_.

RANGE.--Ordovician to Recent: majority of the genera are
Palaeozoic.

PRINCIPAL GENERA.--_Rhynchonella_ (Fig. 327), _Stenochisma_,
_Stricklandia_, _Conchidium_.

Family. _Terebratulidae_

Shell structure punctate.

Arms supported by a calcareous loop, usually bent back on itself.

(For muscular impressions see p. 502, Figs. 328, 329.)

Beak of ventral valve perforated by foramen, furnished with
deltidium.

RANGE.--Devonian to Recent; maximum development in Mesozoic
times.

PRINCIPAL GENERA.--_Terebratula_, _Terebratulina_, _Waldheimia_,
_Terebratella_, _Kingena_, _Magas_, _Centronella_.

Family. _Argiopidae_

Large foramen for passage of pedicle. Marginal septa present
in both valves. Calcareous brachial loop follows margin of
shell and is more or less fused with the septa. Shell structure
punctate.

RANGE.--Jurassic to Recent.

PRINCIPAL GENERA.--_Argiope_, _Cistella_.

Family. _Stringocephalidae_

Shell subcircular, punctate. Cardinal process highly developed,
bifid. Brachial apparatus composed of two calcareous free
lamellae, prolonged at first downwards, then bent back, upwards
and outwards to run parallel to margin of shell and to unite in
front, thus constituting a wide loop.

RANGE.--Silurian and Devonian.

SOLE GENUS.--_Stringocephalus_.

Family. _Thecidiidae_

Shell usually fixed by beak of ventral valve, plano-convex.
Sub-cardinal apophysis in ventral valve for attachment of
occlusors. Marginal septa in dorsal valve. Calcareous brachial
loop more or less fused with shell, and with calcareous spicules
of mantle. Shell structure: inner layer fibrous, outer layer
tubulated.

RANGE.--Carboniferous to Recent.

PRINCIPAL GENERA.--_Thecidium_, _Oldhamina_.

STRATIGRAPHICAL DISTRIBUTION OF BRACHIOPODA

It is remarkable that some of the earliest types of Brachiopoda exist generically unchanged at the present day. Such are _Lingula_, ranging from the Cambrian; _Discina_ and _Crania_, ranging from the Ordovician; and amongst the hinged forms _Terebratula_ from the Devonian, and _Rhynchonella_ from the Ordovician.

In the lowest Cambrian (Olenellus beds) the most important genera are _Linnarssonia_ and _Kutorgina_. The hinged forms appear in the Cambrian, being represented by _Orthis_; but the majority in this formation belong to the Ecardines. _Lingula_, _Lingulella_, and _Obolella_ are characteristic.

In the Ordovician many new genera of the Testicardines make their appearance, such as _Strophomena_, _Leptaena_, _Atrypa_, _Rhynchonella_, _Clitambonites_, etc., but the extraordinary abundance and variety of _Orthis_ is most remarkable. The Ecardines are reinforced by such forms as _Trematis_ and _Siphonotreta_. It is, however, in the Silurian that the Testicardinate Brachiopoda attain their maximum, for in addition to a great development of species amongst the older forms, a host of new genera for the first time occur here (_Spirifera_, _Athyris_, _Conchidium_, _Stricklandia_, _Chonetes_, _Cyrtia_, etc.); and the _Trimerellidae_ are especially characteristic of the Wenlock.

With the commencement of Devonian times many species and genera become extinct, but new forms come in (_Terebratula_, _Orthothetes_, _Productus_, etc.), and some genera are wholly confined to this formation (_Uncites_, _Stringocephalus_). The Carboniferous is marked by the maximum development of _Productus_ and _Spirifera_; _Orthothetes_, _Stenochisma_, and _Athyris_ are also abundant, but there is a considerable extinction of the older genera and species, and a great diminution in the number of individuals and species of those that persist.

A further reduction occurs in the Permian, where the most important genera are _Productus_, _Strophalosia_, and _Stenochisma_; but _Aulosteges_ is a new form peculiar to this period. In the Trias a new era commences; the principal families and genera of the older rocks disappear entirely; a few spire-bearing genera persist (_Spiriferina_, _Athyris_), and the genus _Koninckina_ is restricted to this formation.

The enormous development of species of the _Terebratulidae_ and _Rhynchonellidae_ is the most noticeable feature in Jurassic times; and a few ancient types linger on into the Lias (_Spiriferina_, _Suessia_, a sub-genus of _Spirifera_); _Koninckella_ here occurs.

The Cretaceous Brachiopoda are closely allied to the Jurassic; _Magas_ and _Lyra_ are peculiar to the period, and the _Terebratulidae_ and _Rhynchonellidae_ are very abundant, together with the Ecardinate genus _Crania_.

With the commencement of Tertiary times the Brachiopoda have lost their geological importance, and have dwindled down into an insignificant proportion of the whole Invertebrate fauna.

* * * * *

The distribution of the Brachiopoda in past time is shown in the following table:--

+------------------------------------+-----------------------+-----------+-------+ | | Palaeozoic | Mesozoic | | | | | | | | C | | | | | | | | | | | | | a | | | | | | | | | | | | | r | | | | | | | | | | O | | | b | | | | C | | | | | | r | | | o | | | | r | | | | | C | d | S | D | n | | | J | e | T | | | | a | o | i | e | i | P | | u | t | e | | | | m | v | l | v | f | e | | r | a | r | R | | | b | i | u | o | e | r | T | a | c | t | e | | | r | c | r | n | r | m | r | s | e | i | c | | | i | i | i | i | o | i | i | s | o | a | e | | | a | a | a | a | u | a | a | i | u | r | n | | | n | n | n | n | s | n | s | c | s | y | t | | ECARDINES +---+---+---+---+---+---+---+---+---+---+---+ | Lingulidae Lingula |___|___|___|___|___|___|___|___|___|___|___| | Lingulella |___| | | | | | | | | | | | Obolidae Obolus | |___|___| | | | | | | | | | Obolella |___|___| | | | | | | | | | | Kutorgina |___|___| | | | | | | | | | | Linnarssonia |___| | | | | | | | | | | | Trematis | |___|___| | | | | | | | | | Siphonotreta | |___|___| | | | | | | | | | Acrotreta | |___| | | | | | | | | | | Discinidae Discina | |___|___|___|___|___|___|___|___|___|___| | Craniidae Crania | |___|___|___|___|___|___|___|___|___|___| | Trimerellidae Trimerella | | |___| | | | | | | | | | Dinobolus | |___| | | | | | | | | | | | | | | | | | | | | | | | TESTICARDINES | | | | | | | | | | | | | Productidae Productus | | | |___|___|___| | | | | | | Chonetes | | |___|___|___| | | | | | | | Strophalosia | | | |___|___|___| | | | | | | Strophomenidae Orthis |___|___|___|___|___| | | | | | | | Skenidium | |___|___| | | | | | | | | | Clitambonites | |___| | | | | | | | | | | Strophomena | |___|___| | | | | | | | | | Stropheodonta | |___|___|___| | | | | | | | | Leptaena | |___|___|___|___| | | | | | | | Orthothetes | | | |___|___|___| | | | | | | Davidsonia | | | |___| | | | | | | | | Koninckinidae Koninckina | | | | | | |___| | | | | | Koninckella | | | | | | | |___| | | | | Spiriferidae Spirifera | | |___|___|___|___| | | | | | | Spiriferina | | | |___|___|___|___|___| | | | | Cyrtia | | |___|___|___| | | | | | | | Syringothyris | | | | |___| | | | | | | | Uncites | | | |___| | | | | | | | | Athyris | | |___|___|___|___|___| | | | | | Merista | | |___|___| | | | | | | | | Retzia | | |___|___|___|___|___| | | | | | Atrypidae Atrypa | |___|___|___|___|___|___| | | | | | Dayia | | |___| | | | | | | | | | Coelospira | | |___| | | | | | | | | | Rhynchonellidae Rhynchonella | |___|___|___|___|___|___|___|___|___|___| | Stenochisma | | | |___|___|___| | | | | | | Stricklandia | | |___| | | | | | | | | | Conchidium | | |___|___| | | | | | | | | Terebratulidae Terebratula | | | |___|___|___|___|___|___|___|___| | Terebratulina | | | | | | | |___|___|___|___| | Waldheimia | | | | | | | |___|___|___|___| | Terebratella | | | | | | | |___|___|___|___| | Kingena | | | | | | | |___|___| | | | Magas | | | | | | | | |___| | | | Centronella | | |___|___|___| | | | | | | | Argiopidae Argiope | | | | | | | |___|___|___|___| | Cistella | | | | | | | |___|___|___|___| | Stringocephalidae Stringocephalus | | | |___| | | | | | | | | Thecidiidae Thecidium | | | | | | |___|___|___|___|___| | Oldhamina | | | | |___| | | | | | | | | | | | | | | | | | | | +------------------------------------+---+---+---+---+---+---+---+---+---+---+---+

PHYLOGENY AND ONTOGENY

Wherever successive stages in the life history of an individual resemble in important anatomical features the adult individuals of other species occurring in successive members of a stratigraphical series, the development of the individual may be regarded as an epitome of the development of the species; it also generally throws light on the origin and relationships of allied genera and families.

In the case of the fossil Brachiopoda comparatively little work has yet been done in tracing their ontogeny or phylogeny, though the abundance, variety, and excellent state of preservation of the extinct species offer a promising field for investigation. It is to Dr. C. E. Beecher and other recent American palaeontologists that we owe our advance in this branch of the subject.

In the first place, in about forty genera, representing nearly all the leading families of the group, the important fact has been established of the presence of a common form of embryonic shell, termed the “protegulum,” which is “semicircular or semielliptical in shape with a straight or arcuate hinge line and no hinge area” (Beecher).[431] Its minute size and delicate texture cause its preservation to be rare, but its impression is not uncommonly left on the beak of the adult shell.

The main features of this embryonic shell are exhibited in the adult Lower Cambrian Brachiopod _Obolus_ (_Kutorgina_) _labradoricus_ (Billings); the sub-equal semielliptical valves have lines of growth running concentrically and parallel to the margin of the shell, and ending abruptly against the straight hinge line; and this indicates that there has been no change in the outline and proportions of the shell during its stages of growth, but only a general increase in size. It is very significant that we have here a mature type possessing the common embryonic characters of a host of widely separated genera, and we may therefore regard it as the most primitive form known.

Many genera pass through this so-called “Paterina” stage either in the case of both their valves, or more generally in the case of the dorsal valve only; but modifications in the form of the protegulum arise, which are due to the influence of accelerated growth, by which features belonging to later stages become impressed on the early embryonic shell. The most variable and specialised valve--the ventral or pedicle valve naturally exhibits the effect of this influence first and to the greatest extent. The Palaeozoic adult forms of many species represent various pre-adult stages of the Mesozoic, Tertiary, and Recent species, as is especially well shown in the genera _Orbiculoidea_ and _Discinisca_.

In the Strophomenoid shells the protegulum in the dorsal valve is usually normal, but in the ventral valve abbreviation of the hinge and curvature of the hinge line are produced by acceleration of the “Discinoid stage” in which a pedicle notch is present.

No marked variation has yet been noticed in the spire-bearing, or Terebratuloid, or Rhynchonelloid genera.

The form of the shell and the amount of difference in shape and size of the valves seem to be largely due to the length of the pedicle and its inclination to the axis of the body, as evidenced by the development of _Terebratulina_. A series showing progressive dissimilarity of the two valves arising from these causes can be traced from _Lingula_ to _Crania_. The greater alteration that takes place in the ventral valve appears to be due to its position as lower and attached valve. If the pedicle is short a transversely-expanded shell with long hinge line results when the plane of the valves is vertical or ascending, but when the latter is horizontal a Discinoid form is found. This mode of attachment is often accompanied by a more or less plainly developed radial symmetry. Shells with long pedicles, on the other hand, are usually longer than wide.

The character of the pedicle-opening is of great significance from an evolutional and classificatory point of view, for the successive stages through which it passes in embryonic growth are chronologically paralleled by different genera, and are likewise accompanied by the successive acquisition of other important anatomical characters, as has been shown by Beecher and others. The first and simplest type of pedicle opening is in shells with a posterior gaping of the valves, where the pedicle protrudes freely between them in a line with the axis, and the opening is shared by both valves, though generally to a greater extent by the ventral valve. _Paterina_ (_= Obolus labradoricus_) and _Lingula_ furnish examples of this type. In the second type the pedicle opening is restricted to the ventral valve, and the direction of the pedicle makes a right angle with the plane of the valves; in the lower forms the pedicle lies in a slit or sinus (_Trematidae_), but by further specialisation it becomes enclosed by shell growth so as to lie within the periphery, and finally becomes sub-central in some genera (_Discinidae_). The third type shows the pedicle opening confined to the ventral valve and sub-marginal. A pseudo-deltidium may preserve the original opening (_Clitambonites_); or this shelly plate may become worn away or reabsorbed in the adult so that the deltidial fissure through which the pedicle passes remains quite open (_Orthidae_). In the fourth type the incipient stage marks a return to the simple conditions of the first type; but ultimately a pair of deltidial plates develop, and may completely limit the pedicle opening below. Examples of this type are _Spirifera_ and _Rhynchonella_. By means of these four types the Brachiopods have been divided into four Orders: the _Atremata_ (type i.); the _Neotremata_ (type ii.); the _Protremata_ (type iii.); and the _Telotremata_ (type iv.).

The _Telotremata_ were the last to appear, but the four types of pedicle-opening with the various forms of calcareous brachial apparatus were in existence in the Bala period of the Ordovician.

As _Paterina_ is the most primitive form of all, we may place it at the root of the phylogenetic tree. From it sprang the _Atremata_, which gave off the _Neotremata_ and _Protremata_; the most primitive _Neotremata_ seem to be the _Trematidae_, while the connecting link between the _Protremata_ and _Atremata_ is furnished by the _Kutorginidae_. From the genus _Conchidium_ and its allies we may see how the _Rhynchonellidae_ ushered in the _Telotremata_ as an offshoot from the _Protremata_. The _Telotremata_ subsequently gave off two main branches, which became specialised with the loop-bearing and spire-bearing forms respectively.

The evolution and mutual relationships of genera have been indicated with much probability by Hall, Clarke, and others. The Obolelloid type may be connected with the Linguloid by means of _Lingulella_ and _Linyulepis_, while in _Lingula_ itself we find the point of divergence for the ancestors of _Trimerella_, and for a line of variation culminating in _Dignomia_. The Palaeozoic Rhynchonelloids branched off at an early period from the same stock as _Orthis_, and are connecting links between this genus and Mesozoic Rhynchonellae; and a whole series of genera exhibit intermediate stages of structure between the Rhynchonelloid and Pentameroid groups. The Terebratuloids can be traced back to the primitive type _Renssoellaria_; and amongst spire-bearing forms, the protean genus _Spirifera_ can be split up into groups of species which diverge along lines tending to forms no longer congeneric. When we come to deal with specific differences we find frequently such a host of intermediate varieties that the separation of many species, as in the case of Mesozoic Terebratulae, is to a large extent arbitrary and artificial.

INDEX

References to figures are printed in thick type (=248=, =197=);
to systematic position, in italics (_391_, _430_)

_Abralia_, _391_

Absorption of internal portions of shell, 259

Abyssal Mollusca, 374

_Acanthinula_, _441_

_Acanthoceras_, _399_

_Acanthochiton_, =403=, _403_

_Acanthodoris_, _434_

_Acanthopleura_, _403_;
eyes, =188=

_Acavus_, 303, =304=, 335, _441_

_Acera_, 245, _430_

_Achatina_, 278, 328–337, =333=, _442_, =443=;
jaw, =211=;
food, 33;
size of egg, 124;
_A. fulica_, 279

_Achatinella_, 278, =326=, 327, _443_;
radula, =234=;
musical sounds, 51

_Achatinelloides_, 332

_Acicula_, 287, 296, _414_

_Acmaea_, _405_;
radula, 227

_Acme_, _414_

_Acmella_, 314, _415_

_Acroptychia_, 336, _414_

_Acrotreta_, _504_, 508

_Actaeon_, 250, 427, =428=, _429_;
radula, 217, 230;
streptoneurous, 203 n.

_Actaeonella_, _430_

_Actaeonia_, _432_

_Actaeonina_, 250, _429_

_Actinoceras_, _394_

_Actinodonta_, _447_

_Acusta_, 306, 316, 318, _441_

_Adacna_, =12=, 297, _455_

_Adalaria_, _434_

_Adamsiella_, _414_

_Addisonia_, _412_

_Adelphoceras_, _395_

_Adeorbis_, _416_

_Admete_, _426_

_Aegires_, _434_

_Aegista_, 305, 316, _441_

_Aegoceras_, _398_

_Aeolis_, =10=, =152=, _432_;
radula, 217, =229=;
stinging cells, 65;
mimicked by _Sagartia_, 68;
warning coloration, 72

_Aerope_, 328, 333, _440_;
radula, 215;
habits, 54

Aestivation, 25

_Aetheria_, 328–336, _452_;
variation, 92

_Africarion_, 333, _440_

_Agaronia_, _426_

Age of snails, 39

Aglossa, 7

Agnatha, habits, 51

_Akiodoris_, _434_

_Alaba_, _415_

_Alaria_, _418_

_Alariopsis_, _420_

_Albersia_, 320

Albino varieties, 87

_Alcadia_, 348–351, _410_

_Alderia_, _432_

_Alexia_, _439_

_Alicia_, _459_

_Allognathus_, _441_

_Allopagus_, _452_

Alloposidae, _384_

_Alvania_, _415_

_Alycaeus_, 266, 302 f., 309, 319, _414_

_Amalia_, _440_

_Amalthea_, 78

_Amaltheus_, _398_

_Amastra_, _443_

_Amaura_, _411_

_Amberleya_, _409_

_Ambonychia_, _449_

_Amicula_, _404_

_Ammonites_, 247, =393=, =398=, _398_;
sutures, =396=;
aptychus, =397=

Ammonoidea, _396_ f.

_Amnicola_, 325, _415_

_Amoria_, radula, 222

_Ampelita_, 335, _442_

_Amphibola_, 10, =18=, _439_;
breathing, 151;
radula, 236

_Amphibulimus_, 352, _442_;
radula, 233

_Amphidoxa_, 358

_Amphidromus_, 301, 305, 317, =310=, 359, _442_;
radula, 233

Amphineura, 8, _400_;
breathing organs, 154, 168;
nervous system, =203=;
genitalia, 145

_Amphipeplea_, _439_

_Amphiperas_, _419_

_Amphisphyra_, _430_

_Amphissa_, _423_

_Amphitretus_, =383=

_Ampullaria_, 17, _416_;
self-burial, 42;
spawn, =125=;
breathing organs, 151, =158=;
jaws, =212=;
shell, =249=, 263;
operculum, =268=;
distribution, 294, 320, 322, 343, 359

_Ampullarina_, 302, _439_

_Ampullina_, _411_

_Amussium_, _450_

_Amycla_, _423_

_Anabathron_, _415_

_Anachis_, _423_

_Anadenus_, 24, _441_

Anal glands, 241

Anal siphon, 164, 173

_Anastomopsis_, _442_

_Anatina_, 274, 275, _459_

Anatinacea, _458_;
gills, 167

_Anaulus_, _414_

_Anchistoma_, 293, 296

_Ancilla_, 267, _426_

_Ancillina_, _426_

_Ancistrochirus_, _391_

_Ancistromesus_, _405_

_Ancistroteuthis_, _391_

_Ancula_, _434_;
radula, 229, 230;
warning coloration, 72

_Anculotus_, _417_

_Ancyloceras_, 247, _399_

_Ancylus_, 19, _439_;
breathing, 162;
hibernating, 27;
radula, =235=

_Aneitea_, 325, _443_

_Angitrema_, 340, _417_

_Anisocardia_, _451_

_Anodonta_, 259, 341, _452_;
shower of, 47;
variation, 92;
_Glochidium_, =147=;
gill, =167=;
otocyst, =197=;
nervous system, =206=;
hinge, 274;
_A. anatina_, 24;
distribution, 282

_Anodontopsis_, _451_

_Anoglypta_, 325, _441_

_Anomia_, =257=, _448_, 464;
intestine, 241;
byssus hole, =262=;
hearing, 196

Anomiacea, _448_

_Anoplophora_, _451_

_Anostoma_, =248=, 266, 356, 358, _442_;
aperture, =63=

_Anthracosia_, _451_

_Anura_, _424_

Anus, 209, 241

_Apera_, 334, _440_

_Aperostoma_, 344, _414_

_Aphanotrochus_, _408_

_Aphelodoris_, radula, 230

_Apicalia_, _422_

Aplacophora, 9, _404_;
radula, 228

_Aplecta_, 354, _439_

_Aplustrum_, =245=, =428=, _430_;
radula, 230

_Aplysia_, 245, =428=, _431_;
stomach, 239;
purple fluid, 65

_Aplysioidea_, _430_

_Aporrhais_, _418_;
radula, 215

_Apricardia_, _455_

Aptychus, =397=

_Aptyxiella_, _417_

_Aptyxis_, _424_

Aral Sea, _Limnaea_ from near, =84=;
_Cardium_ from, 91

_Arca_, =14=, 171, =273=, _448_;
eyes, =191=

Arcacea, _448_

Arcachon, oyster-parks at, 105

_Arcestes_, _397_

_Archidoris_, =434=, _434_;
protective coloration, 73

_Architeuthis_, 378, =390=, _390_;
sucker, =381=

_Arcomya_, _458_

_Arconaia_, 307, _452_

Arctic shells, colour of, 86

_Arcuella_, _422_

_Argiope_, =470=, 472, 479, _487_;
parasite of, 485;
distribution, 486;
fossil, 501, _506_, 508

Argiopidae, _506_, 508

_Argobuccinum_, _420_

_Argonauta_, =383=, _383_;
egg-laying, 127;
hectocotylised arm, 137;
radula, 236

_Arinia_, _413_

_Ariolimax_, _441_, 341;
radula, 233

_Arion_, _440_;
shell, 175, 245, 246;
hardier than _Helix_, 24;
voracity, 30 f.;
egg-laying, 42 f.;
protective coloration, 70;
pulmonary orifice, 160;
food, 179;
smell, 193 f.;
radula, 233;
distribution, 285

_Arionta_, =341=, 353, _441_

_Ariophanta_, 301, =308=, 309, 316, _440_;
protective coloration, 70

Aristotle, on modified arm of polypus, 138

_Artemis_, _454_

_Arthuria_, _403_

_Asaphis_, _456_

_Ascoceras_, _394_

Ascoglossa, 11 n., _431_

Ashford, C., on pulsations of heart in _Helix_, 26;
on homing of _Helix_, 35;
on dart-sac, 143

_Asolene_, _416_

_Aspergillum_, 262, _459_

_Aspidelus_, 329, _440_

_Aspidoceras_, _399_

_Assiminea_, _415_

_Astarte_, _451_

_Asthenothaerus_, _459_

_Astralium_, _409_

_Athoracophorus_, _443_--see _Janella_

_Athyris_, 499, 500, _505_;
stratigraphical distribution, 507, 508

_Atilia_, _423_

_Atlanta_, 421, _422_;
foot, 200

_Atopocochlis_, 330, _441_

Atremata, 511

_Atretia_, distribution, 486, _487_

_Atrypa_, 501, =502=, _505_;
stratigraphical distribution, 507, 508

Atrypidae, 501, 505, 508

_Aturia_, 393, _395_

_Atys_, =428=, _430_

Aucapitaine, H., on tenacity of life, 38

_Aucella_, _449_

_Aulopoma_, 157, 304, _414_;
operculum, =269=

_Aulosteges_, _504_;
stratigraphical distribution, 507

_Auricula_, =439=, _439_

_Auriculella_, 327, _443_

Auriculidae, 17, =18=, =260=, =439=, _439_;
lung, 160;
eyes, 186;
radula, 235

_Austenia_, 301, 304, _440_

_Avellana_, _430_

_Avicula_, 254, 258, =449=, _449_;
eyes, 190;
genital orifice, 242;
_A. margaritifera_, 100

_Aviculopecten_, _450_

_Aviculopinna_, _449_

_Axinus_, _452_

_Azeca_, _442_

Azygobranchiata, 155, 407

_Babinka_, _447_

_Bactrites_, _395_

_Baculites_, _399_

_Baikalia_, 290, _415_

Baird, Mr., on the British Museum snail, 37

_Balea_, _442_;
_B. perversa_, 24, 41

Baltic, fauna of the, 12, 83, 366

_Bankivia_, _408_

_Barbatia_, _448_

_Barleeia_, _415_

Barnacle, Rev. H. G., on musical sounds, produced by Mollusca, 51

Barometers, snails as, 50

_Bartlettia_, _452_

_Basilissa_, 376, _408_

Basommatophora, 11, 19, 181, _438_

_Basterotia_, _451_

Bateson, W., on variation in _Cardium_, 91;
on hearing in _Anomia_, 196

_Bathmoceras_, _395_

_Bathydoris_, _433_

_Bathyteuthis_, _390_

_Batissa_, 320, _453_

_Beddomea_, 304

Beecher on phylogeny, 509

Beetles, prey on Mollusca, 58

_Bela_, _426_;
radula, =219=

_Belemnites_, 380

Belemnitidae, _387_

_Belemnosepia_, _390_

_Bellerophon_, =266=, _407_

_Belopetra_, 380

Belopteridae, _388_

_Belosepia_, 386, _388_

_Beloteuthis_, _390_

_Bembix_, 376, _408_

_Benedictia_, 290, _415_

_Benthobia_, 377

_Benthodolium_, 377

_Berendtia_, _441_

Beudant, experiments on Mollusca, 12

Bideford Bridge and mussels, 117

Binney, Dr., on epiphragm, 28

_Binneya_, 341, _441_

_Biradiolites_, _456_

Birds, devour Mollusca, 56 f.

_Bithynella_, 289, 293, _415_

_Bithynia_, 336, 342, _415_;
stomach, 239;
habitat, 25

_Bittium_, _416_

_Blaesospira_, 346, 351

_Blandiella_, 16, _414_

_Blanfordia_, _414_

Blind Mollusca, 185

Blood, 171

Bodö, land Mollusca, 24

Boeuf and French oysters, 107

_Bolma_, _409_

_Boltenia_, _346_

_Boreofusus_, radula, 221

_Bornella_, _433_;
stomach, 239

_Borsonia_, _426_

_Borus_, 356–358, _441_

_Bourcieria_, 357, _410_

_Bourguetia_, _417_

_Bourguignatia_, 332

Bouvier--_see_ Fischer

_Boysia_, 302, _442_

Brachial apparatus, types of, 500

Brachiopoda, fossil, limestone formed of, 492;
shell, 493, 497;
muscle scars on, 494, 501;
platform, 495;
synopsis of families, 503;
stratigraphical distribution, 506;
phylogeny and ontogeny, 509;
Orders, 511

Brachiopoda, recent, 463;
historical account of, 464;
shell, 465;
body, 469;
digestive system, 471;
body cavity, 472;
heart, 473;
excretory organs, 474;
muscles, 475;
nervous system, 478;
reproductive system, 478;
embryology, 479;
habits, 482;
distribution, 484;
classification, 487;
affinities, 487

_Brachytrema_, _417_

Brackish-water species, 14

Branchiae, 151, 153, 164

Branchial siphon, 155, 164, 173

Braun, on self-impregnation, 44

Breathing organs--_see_ Respiration, Branchiae

_Brechites_, _459_

Breeding, periodicity in, 129

_Broderipia_, _408_

_Brotia_, 305

_Brownia_, 133

_Buccinanops_, _423_

_Buccinopsis_, _424_;
radula, 221, 222;
egg-laying, 128

_Buccinum_, =6=, _424_;
radula, 217;
monstrosity, =251=;
breeding, 129;
osphradium, =195=;
spawn, =126=

_Buliminus_, 24, 278, 285, =295= f., 316, 331, 339, _442_;
protective habits, 70;
_B. pallidior_, 38

_Bulimulus_, 278, 334, 339–359, _442_;
jaw, =211=, 233;
radula, 233;
variation, 87

_Bulimus_, 278, 342–359, =355=, _441_;
radula, 233;
egg, =124=

_Bulinus_--see _Isidora_

_Bulla_, 428, _430_

_Bullia_, =155=, _423_;
habits, 192;
foot, 198;
radula, 221

Bulloidea, _429_

Burrowing Mollusca, 446

Burying propensities of Mollusca, 27, 41

_Busycon_, _424_;
money made from, 97;
egg-capsules, =125=--see _Fulgur_

Butterell, Mr., on habits of _Testacella_, 52

_Byssocardium_, _455_

Byssus gland, 201

_Cadlina_, _434_

_Cadoceras_, =393=

_Cadulus_, 376, _445_

_Caecilianella_, _442_;
habitat, 48;
eyes, 186

_Calcarella_, 133

California, land Mollusca, 280

_Calliostoma_, _408_;
jaws, =212=

_Callistochiton_, _403_

_Callochiton_, _403_

_Callogaza_, _408_

_Callonia_, _442_

_Callopoma_, _409_

_Calma_, protective coloration, 74

_Calybium_, _410_

_Calycia_, 320, _442_

_Calycidoris_, _434_

_Calyptraea_, =248=, _412_

_Camaena_, 305, 306, 315, =316=, _441_

Cambrian, Mollusca of the, 2

_Camitia_, _409_

_Campaspe_, _433_

_Camptoceras_, =302=

_Camptonyx_, 278, =302=, _439_

_Campylaea_, 285, 289 f., =293=, _441_

Canal, 155

_Cancellaria_, _426_

_Canidia_, 16, 305, _423_

Cannibalism in snails and slugs, 32, 33

_Cantharidus_, _408_

_Cantharus_, 275;
radula, =222=

_Caprina_, _456_

_Caprotina_, _456_

_Capulus_, _412_

_Caracolus_, =347=-351, _441_

_Carbonicola_, _451_

Cardiacea, _454_

_Cardiapoda_, _421_

_Cardilia_, _454_

Cardinal plate, 500

Cardinal process, 497, 501

_Cardinalia_, _408_

_Cardinia_, _451_

_Cardita_, =273=, _451_

_Carditella_, _451_

_Carditopsis_, _451_

_Cardium_, =6=, =273=, =455=, _455_;
_C. edule_, =12=, =164=;
modifications, 12;
variation, 84, =91=;
nervous system, 207;
distribution, 292, 297

_Carelia_, 327, _443_

_Carinaria_, =9=, =422=, _422_;
foot, 200

_Carinifex_, _439_

_Carolia_, _448_

_Cartusiana_, 296

_Carychium_, 18, _439_

_Caryodes_, 325, 359, _441_

_Casella_, radula, 230

_Caspia_, 12, 297

Caspian Sea, fauna, 12, 297

_Cassidaria_, _420_

_Cassidula_, =18=, 278, =439=, _439_

_Cassis_, 255, _420_;
radula, =223=

_Castalia_, 344, _452_

_Cataulus_, 157, 266, 304, _414_

Caterpillars mimicking _Clausilia_, 68

_Cathaica_, 316, _441_

_Catinella_, _443_

_Cavolinia_, 158, _436_;
eyes, 186

_Cecina_, _414_

_Cenia_, _432_;
breathing, 152

_Centrodoris_, _434_;
radula, 230

_Centronella_, 499, _506_, 508

Cephalopoda, 378 f.;
defined, 5;
ink, 65;
egg-laying, 127;
embryo, =133=;
branchiae, 168;
osphradium, 195;
foot, 200;
nervous system, 206;
jaws, 213;
radula, 236

_Cepolis_, 349–351, _441_

_Cerastoma_, _423_

_Cerastus_, 331, _441_

Cerata of Nudibranchs, 71, 159

_Ceratites_, _397_, =398=;
suture, =396=

_Ceratodes_, 357, _416_

_Ceres_, =21=, 354, _410_

_Ceritella_, _417_

_Cerithidea_, 260, _417_;
_C. obtusa_, breathing, 152

_Cerithiopsis_, _417_

_Cerithium_, =16=, _416_

_Ceromya_, _458_

_Chaetoderma_, =404=, _404_;
breathing organs, =154=;
nervous system, =203=;
radula, 217, 228

_Chaetopleura_, _403_

_Chama_, 257, 272, 446, _455_

_Chamostrea_, _458_

Changes in environment, effect of, 83 f.

Chank-shell, fishery of, 100

_Charis_, 324, _442_

_Charopa_, 319, 323–327, _441_

_Chascax_, _424_

_Chelinodura_, _430_

_Chelotropis_, 133

_Chenopus_, _418_

Chilidium, 498

_Chilina_, 19, _343_, 358

Chilinidae, _439_;
radula, 236

_Chilotrema_, _441_

China, use of shells in, 101

_Chiropteron_, 133

_Chiroteuthis_, 385, _391_

_Chiton_, =8=, =153=, _403_;
egg-laying, 126;
breathing organs, 153 f.;
eyes, =188=;
osphradium, 195;
radula, =228=;
nervous system, =203=;
valves, =401=, =402=;
girdle, =403=

_Chitonellus_, =404=, _404_;
valves, =401=

_Chittya_, 16, 348, 351, _414_

_Chlamydephorus_, 333, _440_

_Chlamydoconcha_, 175, 245, _453_

_Chlamys_, _450_

_Chloritis_, 306, 311, 319–324, _441_

_Chlorostoma_, _408_

_Chlorostracia_, 307

_Choanomphalus_, 250, 290, _439_

Chondrophora, _389_

_Chondropoma_, 346–355, =348=, _414_

_Chondrula_, 285, =295=, 296, _442_

_Choneplax_, _404_

_Chonetes_, _504_;
stratigraphical distribution, 507, 508

_Choristes_, _420_

_Choristoceras_, _398_

_Chorus_, _423_

_Chromodoris_, _434_;
jaws, =212=;
radula, 230

_Chrysallida_, _422_

_Chrysodomus_, _423_

_Chrysostoma_, _409_

_Cingula_, _415_

_Cingulina_, _422_

_Cionella_, _442_

_Circe_, _454_, =458=

Circulatory system, 169

_Circulus_, _408_

Circumpolar species, 287

_Cirrhoteuthis_, 381, =382=

_Cistella_, 467, =470=, 472, 475, 476, 479, 480, _487_;
larvae, =481=, 483;
parasite of, 485;
distribution, 486;
fossil, _506_, 508

_Cistopus_, _385_

_Cistula_, 349, 351, 355, _414_

Cladohepatica, _432_

_Clanculus_, _408_

Classification, 5, 8;
of Gasteropoda, 8, 11

_Clathurella_, _426_

_Clausilia_, =442=, _442_;
mimicked by caterpillars, 68;
monstrosity, 251;
distribution, 285 f., =294=, 305–318, 332, 339–356;
_C. rugosa_, 24;
_scalaris_, 278

_Clavagella_, 262, _459_

_Clavator_, 335, 359, _441_

_Clavatula_, _426_

_Clavella_, _424_

_Claviger_, 329, _417_

_Clea_, =16=, 305, _423_

_Clementia_, _454_

_Cleodora_, =436=, _436_

_Cleopatra_, 294, 328, 331, 336, _416_

Clessin, on duration of life, 39

_Clessinia_, 12, 297

_Clio_, =436=, _436_

_Cliona_, enemy of oysters, 112

_Clione_, 158, _438_

_Clionopsis_, _437_

_Clitambonites_, 498, _505_;
stratigraphical distribution, 507, 508, 511

_Clithon_, 327, _410_

_Clydonites_, _398_

_Clymenia_, _397_

_Clypidella_, _406_

_Cocculina_, _408_

_Cochlicella acuta_, 278

_Cochliolepas_, 77

_Cochloceras_, _398_

_Cochlodésma_, _459_

_Cochlostyla_, 124, 278, =313=, 315, _441_

Cockles, use of, 101, 118

_Coecum_, 247, =260=, _417_, =418=

_Coeliaxis_, 334, _442_;
habitat, 49

_Coelocentrum_, =353=, _442_

_Coelospira_, _505_, 508

Cold winter, effect on oysters, 112;
on mussels, 116

Collinge, W. E., on growth and burial of shells, 41

_Collisella_, _405_

_Collisellina_, _405_;
radula, 227

_Collonia_, _409_

_Colobocephalus_, _430_

Colour of arctic shells, 86

_Colpodaspis_, _430_

_Columbarium_, _426_

_Columbella_, _423_;
radula, =222=

_Columbellaria_, _420_

_Columbellina_, _420_

_Columna_, 328, =330=, _443_

_Cominella_, =16=, _424_

Composition of shell, 252

_Concha_, 463

_Conchidium_, 497, =498=, 500, _505_;
stratigraphical distribution, 507, 508, 511

_Concholepas_, 267, _423_

_Conidea_, _423_

_Conocardium_, _455_

_Conorbis_, _426_

_Conus_, 247, 275, _426_;
poisonous bite, 65;
tooth, =66=;
shell, =69=, =255=, 260;
mimicked by _Strombus_, 69;
prices given for rare, 121;
spawn, =125=;
radula, 218, =220=;
operculum, =269=

_Cookia_, _409_

_Coptochilus_, 314, _414_

_Coralliophaga_, _451_

_Coralliophila_, 75, _423_

Coralliophilidae, radula, 216

_Corambe_, _434_

_Corasia_, 311, 319–321

_Corbicula_, 15, 288, 292 f., _453_

_Corbis_, _452_

_Corbula_, _456_

_Corilla_, 303

_Corona_, 27, _442_

_Coronaria_, =297=

_Coryda_, 346–351, _441_

_Coryphella_, _432_

_Cosmoceras_, _399_

Cowry used as money, 96

Coyote trapped by _Haliotis_, 57

_Cranchia_, _391_

Crania, 464, =467=, 468, 469, 471, 472, 473, 475, 476, =477=,
_487_;
distribution, 485;
fossil, 493, 494, _504_;
stratigraphical distribution, 506, 507, 508, 510

Craniidae, _487_, 496, _504_, 508

_Cranopsis_, =265=, _406_

_Craspedochiton_, _403_

_Craspedopoma_, 298, _414_

_Craspedostoma_, _408_

_Crassatella_, _451_

_Cratena_, _432_

Crawling of _Helix_, 45

_Cremnoconchus_, 16, 302, _413_

_Crenatula_, 75, _449_

_Crenella_, _449_

_Crenipecten_, _450_

_Crepidula_, =248=, 257, =412=, _412_;
parasitic, =78=

_Crepipatella_, =248=, _412_

_Creseis_, =436=, _436_;
eyes, 186

_Crimora_, _434_;
radula, 229

_Crioceras_, 247, =399=, _399_

_Cristigibba_, 311, 319, 320, _441_

_Crossostoma_, _408_

_Crucibulum_, =248=, _412_

_Cryptochiton_, 245, 371, 402, _404_

_Cryptochorda_, _425_

_Cryptoconchus_, _404_

_Cryptophthalmus_, _430_

_Cryptostracon_, 353, _441_

Ctenidia, 151--_see_ Branchiae

_Ctenopoma_, 346–351, _414_

_Cucullaea_, 274, _448_

_Cultellus_, _457_

_Cuma_, _423_

_Cumingia_, _453_

_Cuspidaria_, _459_;
branchiae, 168

_Cuvierina_, =436=, _436_

_Cyane_, _410_

_Cyathopoma_, =247=, 268, 314, 338, _414_

_Cyclas_, _453_;
veliger, =132=;
ova, 146;
otocyst, =197=;
_C. cornea_, thread-spinning, 29;
distribution, 282

_Cyclina_, _454_

Cyclobranchiata, 156

_Cyclocantha_, _409_

_Cyclomorpha_, _414_

_Cyclonassa_, _423_

_Cyclonema_, _409_

Cyclophoridae, origin, 21

_Cyclophorus_, 302, =306=-319, 329–334, 344, 352–358, _414_;
jaws, =212=;
radula, =21=

_Cyclostoma_, 328, 331–338, =414=, _414_;
stomach, 239;
vision, 184;
osphradium, 195;
nervous system, =205=;
_C. elegans_, 287, 288

Cyclostomatidae, origin, 21;
radula, 224;
gait, 199

_Cyclostrema_, _408_

_Cyclosurus_, =247=, 337, _414_

_Cyclotopsis_, 338, _414_

_Cyclotus_, 296, 319, 320, _414_

_Cylichna_, =428=, _430_;
radula, 215

_Cylindrella_, =247=, =260=, 278, 343–355, =348=, _442_;
monstrosity, 251, =252=

Cylindrellidae, radula, 233, =234=

_Cylindrites_, _430_

_Cylindrobulla_, _430_

_Cylindromitra_, _425_;
radula, 222

_Cymbium_, 255, 367, _425_;
radula, =221=

_Cymbulia_, _437_

_Cymbuliopsis_, _437_

_Cynodonta_, _424_

_Cyphoma_, _419_

_Cypraea_, =178=, _419_;
prices given for rare, 122;
mantle-lobes, 177, =178=;
radula, =224=;
shell, =255=, 260, =261=;
_C. moneta_, 96

_Cypraecassis_, _420_

_Cypraedia_, _419_

_Cypraeovula_, _419_

_Cyprimeria_, _454_

_Cyprina_, _451_

_Cyrena_, 15, _453_;
distribution, 285, 294

_Cyrenella_, _453_

_Cyrtia_, _505_;
stratigraphical distribution, 507, 508

_Cyrtoceras_, _394_

_Cyrtodaria_, _457_

_Cyrtodonta_, _452_

_Cyrtolites_, _407_

_Cyrtonotus_, _448_

_Cyrtotoma_, _414_

_Cysticopsis_, 346–351, _441_

_Cystiscus_, _425_

_Cystopelta_, 325, 326, _440_

_Cytherea_, =454=, _454_

_Dacrydium_, _449_

_Daedalochila_, _441_

Dall, W. H., quoted, 35;
on branchiae, 164

_Damayantia_, _440_

_Daphnella_, _426_

Darbyshire, R. D., on tenacity of life, 39

_Dardania_, _415_

Dart-sac, 142

_Daudebardia_, =289=, 292 f., _440_

_Davidsonia_, _505_, 508

_Dawsonella_, _410_

_Dayia_, _505_, 508

Decapoda, _385_ f.

Decollation, 260

Deep-sea Mollusca, 374

De Folin, experiment on _Cyclostoma_, 157

_Deianira_, _410_

Delage, experiments on otocysts, 197

_Delphinula_, _409_

Deltidium, 499

_Dendronotus_, _433_;
protective coloration, 72;
habits, 51

_Dentalium_, =6=, =444=, _445_;
used as money, 97;
veliger, =131=;
radula, =228=

_Dentellaria_, =350=-355, _441_;
aperture, =63=

Desert species, 25, 85