Chapter III: Front Matter (3)

Whilst this dipleuric or bilateral (commonly obliquely ovate or nearly triangular) form of the sagittal ring is distinctly preserved in by far the greater number of #Stephoidea#, it is replaced in some few genera by a more regular, amphithect, diphragmatic, or biradial form. In this case we may often suppose a primary regularity to exist, the dorsal and ventral parts being not yet differentiated, as in _Archicircus_ and _Lithocircus_, _Zygostephanus_ and _Protympanium_, and perhaps also in some other forms. But in other cases the regularity is, on the contrary, secondary, being derived from original bilateral forms.

The rod of the sagittal ring is either cylindrical (with circular transverse section) or angular (commonly with triangular transverse section). In nearly all #Stephoidea# (with very few exceptions) branches or apophyses are developed from the ring, regularly disposed and often of great morphological importance. Commonly these {934}apophyses are developed in pairs, growing symmetrically on both sides of the ring. The most important of these apophyses are:--(1) Basal apophyses, arising from the basal hole of the ring; (2) mitral apophyses, arising from the apical pole; (3) dorsal apophyses, arising from the middle of the dorsal rod; and (4) ventral apophyses, arising from the middle of the ventral rod. The two former arise in the principal axis, the two latter in the sagittal axis of the body. Very frequently the latter pair is replaced by two pairs of transverse branches, one inferior (mandibular) and one superior (orbital). The apophyses of the ring are either simple or branched, often very large, richly ramified, and give origin to a number of further products.

Whilst in the Stephanida the primary sagittal ring alone represents the whole skeleton, it produces in all other #Stephoidea# one or more secondary rings. The most important of these is the horizontal basal ring, appearing first in the Semantida (Pl. 92). From the base of the sagittal ring there arise in the horizontal basal plane two pairs of lateral branches or "basal apophyses." The curved opposite branches of the corresponding pairs become united on each side of the primary ring (right and left), and so produce a second, horizontal ring, perpendicular to the former. This basal ring encloses two paired basal gates, which are enclosed on the medial side by the basal rod of the sagittal ring, and on the lateral side by two united apophyses (_Semantis_, Pl. 92, figs. 1, 2). These two primary basal gates are of the greatest morphological importance; we call them the "jugular gates or jugular pores" (in the description of Bütschli, the pores I, _loc. cit._, p. 498). The dorsal pair of basal apophyses (on their posterior edge) are the coracal rods, _e_ (rods _e_ of Bütschli); the opposite ventral pair (on their anterior edge) are the clavicular or furcular rods, _f_ (rods _e_1 of Bütschli); compare Pls. 92-95, and their explanation.

The skeleton of _Semantis_, the prototype of the Semantida, thus assumes the characteristic form of a signet-ring. The basal ring enclosing the two jugular pores corresponds to the seal-plate. It is commonly more or less horizontal; but often the apophyses descend obliquely (Pl. 92, figs. 1, 2, 13, &c.), more rarely laterally (Pl. 29, fig. 11). The further development of this typical form is essentially effected by the production of new basal pores in the horizontal seal-plate. In _Semantrum_ (Pl. 92, figs. 3, 4, 5) we find already four basal gates. Behind the jugular gates is formed a second pair, the "cardinal gates" (pores II of Bütschli). These are enclosed on the anterior margin by the coracal rods (_e_), on the posterior margin by the scapular rods (_d_), a third pair of basal apophyses, arising behind the former from the sagittal ring and uniting with them (the rods _e_2 of Bütschli). Commonly the two posterior, or cardinal gates are much larger than the two anterior, jugular gates. This characteristic basal plate of _Semantrum_, with two pairs of basal pores, is of the greatest morphological importance, as it is inherited in by far the greater number of the NASSELLARIA, though not so generally as Bütschli supposes. The basal ring of _Semantrum_ is either more circular {935}or elliptical, or more polygonal, and is connected with the basal rod of the sagittal ring by three pairs of radial apophyses, the anterior furcular, the middle coracal, and the posterior scapular rods.

A third important form of Semantida is _Semantidium_ (Pl. 92, figs. 6, 7). Here we find three pairs of basal pores in the seal-plate; the third pair, newly formed, consists of the cervical gates (_e_), bounded in front by the scapular rods (_d_), behind by a fourth pair of basal apophyses, the cervical rods.

The basal apophyses of the sagittal ring are not only of great morphological importance, because they produce by their union three typical pairs of basal gates or "collar pores," but also because their prolongations often appear as typical basal feet. The distal prolongations of the coracal rods appear in _Semantiscus_ (Pl. 92, figs. 16-18) as two pectoral feet, those of the scapular rods as two tergal feet, whilst the opposite prolongations of the basal rod of the sagittal ring appear as two "sagittal feet" (in front an anterior or sternal, and behind a posterior or caudal foot). In the typical _Cortiniscus_ (Pl. 92, figs. 11-13) only three feet are developed; an odd caudal and two paired pectoral feet (compare above, p. 891). The typical basal ring of the Semantida, with its paired basal gates (_Semantis_), reappears in the majority of the Coronida, differing from the former in the development of a second vertical ring, which lies in the frontal plane (perpendicular to the sagittal ring), and which we therefore call the frontal ring. In only one small group of the Coronida the basal ring is absent, namely, in the Zygostephanida, and here the frontal ring appears in the simplest form, as a complete elliptical meridian ring, crossing the sagittal ring perpendicularly on the two poles of the main axis (_Zygostephanus_, Pl. 93, figs. 1-4), Four large lateral gates between the two rings remain open. This form may be derived directly from the Stephanida in the following way; from both poles of a simple sagittal ring there arise two opposite lateral apophyses, which in the frontal plane become curved one towards the other, and united in the poles of the transverse axis. The basal apophyses would be the coracal rods. But it is also possible that _Zygostephanus_ was derived from _Semantis_ by the loss of the furcular rods.

The three typical rings (or the "dimensive rings") of the #Stephoidea# appear in their most complete form in the subfamily Trissocyclida (Pl. 93, figs. 7, 13). Here all three rings are undivided and completely developed in the three dimensive planes, perpendicular one to another. Between them there remain eight large open gates; the four superior are the four "lateral gates" of _Zygostephanus_, the four inferior are the four basal gates of _Semantrum_. The four latter are originally much smaller than the four former; but in _Trissocircus_ and _Trissocyclus_ (Pl. 93, figs. 10-12) they reach the same size. Therefore all eight gates are here of equal form and similar size, and the basal ring, now a true equatorial ring, divides the two meridional rings into two equal halves.

In the Eucoronida, a third subfamily of Coronida, the sagittal and the basal rings {936}are complete, but the frontal ring is incomplete, its basal part being wanting (Pl. 82, figs. 4-6). Therefore we find here six large gates between the three rings; four upper lateral gates (between the two crossed vertical rings) and two lower basal gates (between the basal rod of the sagittal ring and the two halves of the basal ring). _Eucoronis_, the type of this subfamily, may be derived either directly from _Semantis_ by development of a frontal ring, or from _Tristephanium_ by loss of the basal part of the frontal ring.

A quite simple basal ring with a single gate, distinguishes the fourth subfamily of Coronida, the Acanthodesmida (_sensu restricto_), the genera _Coronidium_ (Pl. 82, figs. 1, 2, 7, 8) and _Acanthodesmia_ (Pl. 93, fig. 5). The horizontal basal ring alone is here complete, whilst both vertical rings (the sagittal and frontal rings) are incomplete, their basal parts being wanting. Therefore there are here five gates, four lateral and one basal. These forms may be derived from _Eucoronis_ by loss of the basal rod of the primary sagittal ring.

The Tympanida, the fourth family of #Stephoidea#, exhibit another type of ring structure. Here two parallel horizontal rings are constantly developed, one on the apical pole, the other on the basal pole of the sagittal ring. The latter is the same basal ring as in the Semantida and Coronida. The former is a "mitral ring," developed in the same manner, by union of two pairs of horizontal lateral branches, which arise on both sides from the apical rod (or mitral rod) of the sagittal ring. In the simplest case these two parallel horizontal rings are connected only by the sagittal ring, which is either complete (_Protympanium_, Pl. 93, fig. 14) or incomplete (_Parastephanus_, Pl. 93, fig. 21). But commonly also an incomplete frontal ring is present, so that the two horizontal rings are connected by four vertical or subvertical rods; two of these "columellæ" are the dorsal and ventral rods of the sagittal ring, the two others are the lateral rods of the frontal ring. Between the former and the latter are sometimes developed two, four, or more accessory columellæ (probably halves of accessory incomplete diagonal meridian rings). In this way arise the characteristic "drum-forms" of many Tympanida, in which the two parallel horizontal rings correspond to the upper and lower rings of a drum, whilst the connecting vertical columellæ correspond to its parallel lateral rods (Pl. 83, figs. 1, 2, &c.).

Originally the two horizontal rings of these "drum-shells" are both bisected by the complete sagittal ring, each provided with two lateral gates (Protympanida). But in the Eutympanida both rings exhibit one simple gate only, the apical and the basal rod of the sagittal ring being lost. In the Paratympanida both rings are closed by a secondary lattice-plate whilst in the Dystympanida the upper (mitral) ring alone is closed by such a plate, the lower (basal) ring is open. In some Eutympanida the shell assumes the strange form of a regular geometrical cube, the twelve edges of which are represented by thin rods of silex (_Lithocubus_)--its four upper edges represent the mitral ring, the four lower the basal ring; two opposite of the four vertical {937}cube-edges are the lateral halves of the frontal ring, the two other alternate ones are the remaining halves of the reduced sagittal ring (dorsal and ventral rod) (Pl. 82, fig. 12).

In many Tympanida and Coronida a loose irregular lattice or framework is developed, which partly closes the large open gates. But this never reaches the completeness of a true lattice-shell, such as we find in the #Spyroidea#, #Botryodea#, and #Cyrtoidea#. In by far the greater number of #Stephoidea# the corners, and partly also the rods, of the shell are armed with numerous irregular spines, often forked or richly branched. Among these spines the descending "basal apophyses" possess a peculiar importance, since by their regular number and disposition they correspond to the radial rods of the #Plectoidea#, and to the typical "feet" of the #Spyroidea# and #Cyrtoidea#. The most important of them are the three cortinar feet (one caudal and two pectoral) of _Cortina_, _Cortiniscus_, &c. (compare above, p. 891).

_The Central Capsule_ exhibits in the #Stephoidea# the same characteristic structure as in all other MONOPYLEA, first exactly pointed out by Richard Hertwig in 1879 (Organismus der Radiol., p. 71, Taf. vii. figs. 4, 5). Its form is commonly ovate or ellipsoidal, sometimes also lentelliptical or nearly spherical. It exhibits constantly on the basal pole the porochora or porous area, and in the basal half the podoconus or pseudopodial cone. From the surrounding sagittal ring it is separated by a thick jelly-like calymma, which commonly exhibits numerous zooxanthellæ. The numerous pseudopodia are commonly branched, with rather rare anastomoses. The membrane of the central capsule is thick.

_Synopsis of the Families of_ #Stephoidea#.

I. Skeleton composed of the simple vertical sagittal ring
only, without secondary rings, 1. STEPHANIDA.

II. Skeleton composed of two crossed rings, a vertical
sagittal and a horizontal basal ring, 2. SEMANTIDA.

III. Skeleton composed of two crossed vertical meridional
rings (a primary sagittal and a secondary frontal ring),
commonly also with a horizontal basal ring, 3. CORONIDA.

IV. Skeleton composed of two parallel horizontal rings
(upper mitral and lower basal ring), both connected by
a vertical sagittal ring (and often by a vertical
frontal ring), 4. TYMPANIDA.

Family XLVIII. #STEPHANIDA#, Haeckel (Pl. 81).

_Monostephida_, Haeckel, 1881, Prodromus, p. 447.

_Definition_.--#Stephoidea# with a simple sagittal ring, without any lattice-work.

The family #Stephanida# is the most simple of all #Stephoidea#, and probably the common ancestral group of this suborder (compare above, p. 933). The skeleton {938}consists of a simple ring only, surrounding the central capsule, and armed commonly with simple thorns or with larger branched spines. The branches of these spines are constantly free, never joining together. Therefore the shell exhibits no trace of fenestration or lattice-work, no pores or gates, except the simple large gate of the ring itself. In all other #Stephoidea# we find secondary gates or lattice-work.

The first known form of this family is _Lithocircus annularis_, described by Johannes Müller in 1858 (Abhandl. d. k. Akad. d. Wiss. Berlin, p. 29, Taf. i. fig. 1). He observed already the central capsule ("Blase") surrounded by the circular ring of silex, and the calymma ("Strahlige Gallert") enveloping the whole body. The peculiar structure of the soft body, particularly the "area porosa" on the basal pole of the central capsule, and the pseudopodial cone within it, were first accurately described by Hertwig (in 1879). A great number of simple rings, similar to these, were found in the Challenger collection, and are here arranged in six genera and forty-eight species.

The simple ring of silex, which alone forms the skeleton of the Stephanida, corresponds to the primary or sagittal ring of the other #Stephoidea#, and lies therefore vertically in the median or sagittal plane of the body. We can therefore distinguish on it four different segments, rods or bows, two of which are more horizontal, two more vertical. The former are one upper bow or apical rod, and one lower bow or basal rod. The latter are one posterior bow or dorsal rod, and one anterior bow or ventral rod. Sometimes each of these four component bows is distinguished by a corner-spine, or by a pair of divergent branches.

In the two simplest (and probably oldest) genera of Stephanida, in _Archicircus_ and _Lithocircus_, the dorsal and ventral rods of the ring are equal and cannot be distinguished; therefore the fundamental form is here amphithect, diphragmatic, or biradial (the poles of the sagittal axis being equal). In the four other genera the dorsal rod is more straight (often vertical) and more or less different from the ventral, convexly curved rod; therefore the fundamental form is here dipleuric or bilateral, as in the greater number of all NASSELLARIA (the poles of the sagittal axis being unequal). The general form of the ring in this latter case is commonly obliquely ovate or nearly triangular, the basal pole being more pointed, the apical pole more rounded (Pl. 81).

The rods or bows of the ring are either roundish or cylindrical (with circular or elliptical transverse section), or they are prismatic or angular (commonly with triangular transverse section). In the latter case one edge usually is prominent in the sagittal plane (on the convex outside of the ring), whilst two other edges diverge laterally on both sides of it. The inner or concave margin of the ring is commonly smooth.

The inner perimeter of the large gate, enclosed by the ring, is commonly rounded (elliptical or ovate), rarely angular. However, the outer perimeter of the ring is {939}nearly always polygonal, with prominent corners, and usually from these arise thorns or branched spines which are regularly disposed. Regarding this disposition we may distinguish three cases: A, the spines lie in the sagittal plane and form a single row, arising from the median edge; B, the spines lie on both sides of the latter and form two parallel rows, arising from the two lateral edges; C, the spines represent a combination of A and B, and are disposed in three rows, two paired rows arising from the two lateral edges, and an odd middle row between them, arising from the median edge. The spines are simple, without branches, in _Archicircus_ and _Zygocircus_; more or less branched in _Lithocircus_ and _Dendrocircus_. The branches are often richly ramified or arborescent, and exhibit great variety in size, special form, and direction (compare Pl. 81).

The number and disposition of the spines or groups of spines are usually constant, and may be employed in the further progress of our knowledge, to distinguish a number of genera and subgenera. Very commonly (perhaps in the majority of the Stephanida) we find six groups of spines, an apical group on the upper rod of the sagittal ring, a basal group on the lower rod (on the porochora of the central capsule), two ventral groups on the anterior rod, and two dorsal groups on the posterior rod. In other species we find four or eight groups instead of six, and sometimes a larger number.

The most important of these apophyses of the ring are the basal spines, arising from its basal pole, where the porochora of the central capsule rests upon it. They are often much larger and more branched than the other spines, and attain a peculiar morphological value in the small subfamily Cortinida. Here we find three or four regularly disposed "basal spines," which may be compared to the typical "basal feet" of the #Cyrtellaria#, appearing in the majority of #Spyroidea# and #Cyrtoidea#. _Cortina_, one of the most important NASSELLARIA, bears three typical divergent feet on the base of the simple ring, two paired anterior or "pectoral feet," and an odd posterior or "caudal foot." The latter appears as a direct basal prolongation of the dorsal rod of the ring, and is opposed to an upper prolongation of the same, which corresponds to the "apical horn" of the #Cyrtellaria# (Pl. 97, figs. 1-3). As already explained above, these three basal feet of _Cortina_ possess the highest phylogenetic value, since they may also be compared with the three primary radial spines of the #Plectoidea#, and so connect the #Cyrtellaria# and the #Plectellaria#. _Stephanium_ differs from _Cortina_ in the possession of four basal feet, an odd anterior or "sternal foot" being added to the three typical feet of the latter (Pl. 92, figs. 20, 21). Some forms of #Plectoidea# (_Plagoniscus_, _Plectaniscus_, &c.) seem to be nearly related to these Cortinida, and may be easily transformed into them by development of a complete ring, embracing the central capsule. They seem to demonstrate the near affinity of all these triradiate NASSELLARIA (Pl. 91, figs. 4, 5, 9, 10).

{940}_Synopsis of the Genera of Stephanida._

-------------------------------------------------------------------------
I. Subfamily Lithocircida.
No typical basal feet on the base of the ring (no cortinar feet).
-------------------------------------------------------------------------
Ring diphragmatic or { Ring smooth or thorny,
amphithect; dorsal { without branched spines. 401. _Archicircus_.
and ventral bow {
equal. { Ring armed with branched
{ spines, 402. _Lithocircus_.

Ring dipleuric, { Ring smooth or thorny,
bilateral; dorsal { without branched spines, 403. _Zygocircus_.
and ventral bow {
different. { Ring armed with branched 404. _Dendrocircus_.
{ spines.
-------------------------------------------------------------------------
II. Subfamily Cortinida.
Three or four typical basal feet on the ring (cortinar feet).
-------------------------------------------------------------------------
Three basal feet (and { One caudal and two lateral
an apical horn). { feet, 405. _Cortina_.

Four basal feet (and { Two sagittal and two
an apical horn). { lateral feet, 406. _Stephanium_.

Subfamily 1. LITHOCIRCIDA, Haeckel.

_Definition_.--#Stephanida# without typical basal feet or cortinar feet.

Genus 401. _Archicircus_,[20] n. gen.

_Definition_.--#Stephanida# with a simple amphithect or diphragmatic ring, smooth or thorny, without branched spines and basal feet.

The genus _Archicircus_ is the most primitive and simplest form of all #Stephoidea#, and probably the common ancestral form, not only of this suborder, but of the greater number of all NASSELLARIA (compare above, p. 893). The skeleton consists only of a quite simple sagittal ring, in which commonly a slight difference of both poles of the main axis (basal and apical pole) is visible, but no difference between the dorsal and the ventral bow of the ring. In my Prodromus (1881, p. 447) the species of _Archicircus_ were disposed partly in the subgenus _Monostephus_, partly in the genus _Lithocircus_.

Subgenus 1. _Monostephus_, Haeckel, 1881, Prodromus, p. 447.

_Definition._--Ring circular, elliptical, or ovate, without prominent corners.

1. _Archicircus princeps_, n. sp.

Gate circular. Ring circular, smooth, its transverse section also circular. The simplest form of all #Stephoidea#.

_Dimensions._--Diameter of the gate 0.05 to 0.08; thickness of the ring 0.006 to 0.008.

_Habitat._--Central Pacific, Stations 265 to 274, depth 2350 to 2925 fathoms.

{941}2. _Archicircus monostephus_, n. sp. (Pl. 83, fig. 17).

Gate circular. Ring circular, with three elegantly denticulate edges (one outer median and two lateral edges). Transverse section of the ring triangular.

_Dimensions._--Diameter of the gate 0.06 to 0.08; thickness of the ring 0.01 to 0.008.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

3. _Archicircus ellipsis_, n. sp.

Gate elliptical. Ring elliptical, on the inner margin smooth, on the outer margin with fifteen to twenty equal, short, simple, or slightly forked thorns. Transverse section ovate.

_Dimensions._--Diameter of the gate 0.05 to 0.09; thickness of the ring 0.01 to 0.014.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms; also fossil in Barbados.

4. _Archicircus ovalis_, n. sp.

Gate ovate. Ring elliptical, smooth, with three prominent, slightly distorted edges, without thorns; in the transverse section triangular.

_Dimensions._--Diameter of the gate 0.08 to 0.12; thickness of the ring 0.006 to 0.009.

_Habitat._--Tropical Atlantic, Station 347, depth 2250 fathoms.

5. _Archicircus monopylus_, n. sp.

Gate ovate. Ring ovate, thorny, with three distorted edges, in the transverse section triangular; surface covered with numerous simple small thorns arising from the three edges.

_Dimensions._--Diameter of the gate 0.1 to 0.15; thickness of the ring 0.01 to 0.012.

_Habitat._--Indian Ocean (Madagascar), Rabbe, surface.

Subgenus 2. _Archistephus_, Haeckel.

_Definition._--Ring polygonal, with four to six or more prominent corners (and commonly with simple spines arising from the corners).

6. _Archicircus quadratus_, n. sp.

Gate square. Ring square, with three edges and four short simple pyramidal spines on the four corners, opposite in pairs in two perpendicular diameters. Transverse section triangular.

_Dimensions._--Diameter of the gate 0.08; thickness of the ring 0.008.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

{942}7. _Archicircus rhombus_, n. sp. (Pl. 81, fig. 7).

Gate rhombic. Ring rhombic, with four prominent edges and four pairs of short, divergent, pyramidal spines on the four corners, arising from the lateral edges of the four rods, about as long as the radius of the gate.

_Dimensions._--Diameter of the gate 0.04 to 0.08; thickness of the ring 0.007 to 0.01.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

8. _Archicircus duodenus_, n. sp.

Gate square or rhombic. Ring rhombic, with three prominent edges and twelve stout and straight pyramidal spines, about as long as the radius of the gate. In each of the four corners are three divergent spines, arising from the three edges of each two meeting rods.

_Dimensions._--Diameter of the gate 0.08; thickness of the ring 0.012.

_Habitat._--North Atlantic, surface (Rabbe).

9. _Archicircus primordialis_, n. sp. (Pl. 81, fig. 1).

Gate ovate. Ring hexagonal, with three prominent edges and six short pyramidal thorns at the six corners; the basal thorn is either simple or forked.

_Dimensions._--Diameter of the gate 0.07; thickness of the ring 0.01 to 0.015.

_Habitat._--Central Pacific, Stations 265 to 274, depth 2350 to 2925 fathoms.

10. _Archicircus hexacanthus_, n. sp. (Pl. 81, fig. 4).

Gate subregular, hexagonal. Ring hexagonal, with three sharp edges and six equal radial pyramidal spines, arising from the six corners and placed in the plane of the ring, about as long as the diameter of the gate.

_Dimensions._--Diameter of the gate 0.05 to 0.07; thickness of the ring 0.01.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

11. _Archicircus hertwigii_, Haeckel.

_Lithocircus annularis_, R. Hertwig (_non_ J. Müller), 1879, Organismus
der Radiol., p. 69. Taf. vii. fig. 5.

Gate hexagonal, with prolonged main axis. Ring hexagonal, with two prominent edges and six pairs of equal, short, conical spines, arising from the two edges of the six rods at the six corners and divergent on each side of the plane of the ring. The basal spine-pair is doubled, therefore there are in all fourteen spines.

_Dimensions._--Diameter of the gate 0.05 to 0.07; thickness of the ring 0.005 to 0.006.

_Habitat._--Mediterranean (Messina), Hertwig, surface.

{943}12. _Archicircus triglyphus_, n. sp.

Gate ovate. Ring hexagonal, with three prominent edges and twenty-two to twenty-four simple curved spines, arising from the six corners and about as long as the diameter of the gate. In the basal corner arise six to nine larger spines, protecting the basal pole of the central capsule. From each of the five other corners arise three spines, diverging from the three edges.

_Dimensions._--Diameter of the gate 0.07 to 0.11; thickness of the ring 0.008 to 0.011.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

13. _Archicircus sexangularis_, n. sp. (Pl. 81, fig. 12).

Gate hexagonal or subcircular. Ring hexagonal, with two sharp prominent edges and six pairs of divergent spines, about as long as the radius of the gate, and arising from the two edges at the six corners. The two apical and the two basal spines are simple and conical, whilst the eight other spines, arising in pairs from the two dorsal and the two ventral corners, are slightly forked.

_Dimensions._--Diameter of the gate 0.06 to 0.08; thickness of the ring 0.01 to 0.015.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

Genus 402. _Lithocircus_,[21] J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 484.

_Definition._--#Stephanida# with a simple amphithect or diphragmatic ring, armed with branched spines, without typical basal feet.

The genus _Lithocircus_ is the oldest known form of all #Stephoidea#, founded by J. Müller in 1856 for his _Lithocircus annularis_, the first species of this suborder described. We retain here this cosmopolitan form as the typical representative of the genus, which differs from the preceding _Archicircus_, its ancestral form, in the development of branched radial spines.

1. _Lithocircus annularis_, J. Müller.

_Lithocircus annularis_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 29, Taf. i. fig. 1.

Gate circular. Ring circular, with four forked or simply branched spines, opposite in pairs in two diameters, perpendicular one to the other. Spines with slender curved fork-branches, about as long as the diameter of the gate. The specimen figured by J. Müller bears a supernumerary fifth spine; numerous other specimens observed by me exhibited a regular cross of four spines.

_Dimensions._--Diameter of the gate 0.1 to 0.15; length of the spines 0.01 to 0.18.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

{944}2. _Lithocircus quadricornis_, n. sp. (Pl. 81, fig. 9).

Gate square. Ring square, with three sharp denticulate edges, and four large bunches of richly branched spines on the four corners. In each corner arise three curved spines, about as long as the diameter of the ring; their numerous irregular branches are forked and curved like the antlers of deer.

_Dimensions._--Diameter of the gate 0.07; length of the horns 0.06 to 0.09.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

3. _Lithocircus decimalis_, n. sp. (Pl. 81, fig. 15).

Gate elliptical. Ring pentagonal, with three prominent edges and five pairs of branched spines on the five corners. In each corner arise two or three curved spines, about as long as the radius of the gate, each with two to four forked branches.

_Dimensions._--Diameter of the gate 0.08; length of the spines 0.03 to 0.05.

_Habitat._--North Atlantic, Station 354, surface.

4. _Lithocircus hexablastus_, n. sp. (Pl. 81, fig. 17).

Gate elliptical. Ring hexagonal, with three prominent edges and six pairs of branched spines, arising from the six corners. Each of the twelve spines is short and stout, only half as long as the radius of the gate, and bears a bunch of ten to twenty short, densely aggregated, conical or horn-like curved branches.

_Dimensions._--Diameter of the gate 0.1; length of the spines 0.02 to 0.03.

_Habitat._--Central Pacific, Stations 265 to 268, depth 2700 to 2900 fathoms.

5. _Lithocircus crambessa_, n. sp. (Pl. 81, fig. 6).

Gate elliptical or subcircular. Ring hexagonal, with three wing-shaped distorted edges and six groups of branched spines, arising from the six corners. In each corner arise three short and stout divergent spines, each bearing a bunch of numerous short roundish branches like a cauliflower, scarcely as long as the thickness of the ring.

_Dimensions._--Diameter of the ring 0.1 to 0.12, length of the spines 0.01 to 0.02.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

6. _Lithocircus tarandus_, n. sp. (Pl. 92, fig. 19).

Gate circular. Ring hexagonal, with three sharp edges and six pairs of large branched spines, arising from the flat lateral edges on the six corners. Each of the twelve spines is horizontally expanded, longer than the diameter of the ring and dichotomously forked like the antlers of a {945}reindeer. If the lateral ends of the branches of this species become united in the frontal plane, we get _Microcubus_, the four upper spines forming the mitral ring, the four middle the equatorial ring, and the four lower the basal ring.

_Dimensions_.--Diameter of the gate 0.08; length of the spines 0.09.

_Habitat_.--Central Pacific, Station 272, surface.

7. _Lithocircus furcatus_, n. sp.

Gate ovate. Ring ovate, with three sharp prominent edges. The two lateral edges are smooth. The median edge (in the sagittal plane) bears sixteen to twenty forked spines (commonly eight dorsal, eight ventral, and four basal). All the spines are of nearly equal size, slightly curved, and about half as long as the short sagittal axis of the ring.

_Dimensions_.--Diameter of the gate 0.08 to 0.12; length of the spines 0.03 to 0.04.

_Habitat_.--North Pacific, Station 253, depth 3125 fathoms.

8. _Lithocircus magnificus_, n. sp. (Pl. 81, fig. 16).

Gate ovate or nearly elliptical. Ring ovate, with three prominent edges, and numerous richly branched spines arising from the three edges. The specimen figured, which I observed living in the Mediterranean, exhibited eight bunches of larger spines, three dorsal, three ventral, one apical, and one basal bunch; the latter much larger than the seven others. Each bunch was composed of two to four larger and numerous smaller spines, their branches curved and forked. The ovate purple central capsule, with a distinct podoconus, filled more than the half of the gate.

_Dimensions_.--Diameter of the gate 0.1 to 0.13; length of the spines 0.05 to 0.15.

_Habitat_.--Mediterranean (Portofino, 1880), Atlantic (Canary Islands), Station 354, surface.

Genus 403. _Zygocircus_,[22] Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 496.

_Definition_.--#Stephanida# with a simple dipleuric or bilateral ring, smooth or thorny, without branched spines and basal feet.

The genus _Zygocircus_ and the following _Dendrocircus_ differ from the two preceding older genera in the bilaterally symmetrical or dipleuric form of the sagittal ring. Whilst in _Archicircus_ and _Lithocircus_ the two sagittal halves or bows of the ring, the dorsal and ventral bow, are equal (therefore the fundamental form amphithect or diphragmatic), here both bows become distinctly different; the dorsal bow is constantly more straight (often vertical), the ventral bow more convex (obliquely ascending). This dipleuric differentiation is most important, as it is transmitted to the greater number of NASSELLARIA by heredity.

{946}1. _Zygocircus sagittalis_, n. sp.

Gate ovate. Ring half ovate or nearly triangular, with three curved edges and three prominent corners, one apical and two basal protuberances. Dorsal rod vertical, twice as long as the horizontal basal rod. Ventral rod convexly curved.

_Dimensions._--Diameter of the gate 0.05 to 0.07; height of the tubercles 0.01 to 0.015.

_Habitat._--Central Pacific, Stations 265 to 268, depth 2900 fathoms.

2. _Zygocircus trigonus_, n. sp.

Gate triangular. Ring triangular, with three curved edges and three prominent corners, which are prolonged into nine divergent conical spines; three spines arising from the three edges of each corner. Dorsal rod vertical; ventral and basal rods curved and convergent.

_Dimensions._--Diameter of the gate 0.11 to 0.13; length of the spines 0.01 to 0.015.

_Habitat._--Indian Ocean, Sunda Archipelago (Rabbe), surface.

3. _Zygocircus tetragonus_, n. sp.

Gate ovate. Ring quadrangular, without edges, with four simple conical spines of different sizes; one smaller apical, one larger basal, and two equatorial spines of middle size (one dorsal and one ventral). Dorsal and ventral rod curved.

_Dimensions._--Diameter of the gate 0.04 to 0.06; length of the spines 0.018 to 0.026.

_Habitat._--Tropical Atlantic, Station 338, depth 1990 fathoms.

4. _Zygocircus rhombicus_, n. sp.

Gate rhombic. Ring rhombic, with three prominent edges, and eight short conical curved spines arising from the lateral edges at the four corners of the rhombus. The basal and ventral spine are larger than the apical and dorsal spine; the ventral rod is more curved (with smaller angle) than the shorter dorsal rod. The medial edge of the ring is smooth, without spines.

_Dimensions._--Diameter of the gate 0.08; length of spines 0.02 to 0.04.

_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.

5. _Zygocircus pentagonus_, n. sp. (Pl. 81, fig. 8).

Gate roundish pentagonal. Ring very thick (about as thick as the radius of the gate), irregularly pentagonal, with prominent sagittal edge. On both sides of the latter arise at the five corners five pairs of short simple irregularly curved spines. The four ventral spines are larger than the four dorsal, and the two basal spines larger than the eight former, forked. (In fig. 8 the basal spines are turned upwards.)

_Dimensions._--Diameter of the gate 0.07; length of the spines 0.04 to 0.06.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

{947}6. _Zygocircus hexagonus_, n. sp.

Gate irregularly hexagonal. Ring obliquely hexagonal, thick, without edges, with six short and stout conical spines on the six corners. The two spines of the curved ventral rod are longer than the two spines of the straight dorsal rod. The apical spine is smaller and the basal spine larger than the four others.

_Dimensions_.--Diameter of the gate 0.07 to 0.09; length of the spines 0.01 to 0.03.

_Habitat_.--North Pacific, Station 241, depth 2300 fathoms.

7. _Zygocircus triquetrus_, n. sp. (Pl. 81, fig. 3).

Gate obliquely ovate. Ring obliquely hexagonal, with three sharp edges and three short conical spines on each of the six corners. Therefore each hexagonal edge bears six short radial spines of equal size.

_Dimensions_.--Diameter of the gate 0.04 to 0.08; length of the spines 0.01 to 0.02.

_Habitat_.--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

8. _Zygocircus dodecanthus_, n. sp.

Gate semicircular. Ring semicircular or irregularly hexagonal, without edges, with twelve short blunt spines, arising in pairs from the six corners; two apical, two basal, and between them two equatorial corners. Three pairs of spines remain on the straight dorsal rod, three on the curved ventral rod.

_Dimensions_.--Diameter of the gate 0.04 to 0.06; length of the spines 0.01 to 0.02.

_Habitat_.--Central Pacific, Stations 263 to 268; depth 2650 to 2900 fathoms.

9. _Zygocircus acacia_, n. sp. (Pl. 81, fig. 5).

Gate obliquely ovate. Ring semi-ovate, with straight dorsal and curved ventral rod, partly with distorted edges. Six bunches of numerous short and straight conical spines arise from the ring, one larger bunch (often trifid) from the apex, two smaller bunches from the dorsal, two from the ventral rod, and one very large bunch from the base. The six bunches are often more separated, smaller, and the spines shorter than in the figured specimen, which passes over into _Dendrocircus_.

_Dimensions_.--Diameter of the gate 0.12 to 0.16; length of the spines, 0.01 to 0.07.

_Habitat_.--Central Pacific, Station 266, depth 2750 fathoms.

10. _Zygocircus polygonus_, n. sp. (Pl. 81, fig. 2).

Gate irregularly roundish or ovate. Ring irregularly polygonal or sometimes nearly circular, without edges, armed with a single series of ten to fifteen short pyramidal spines, which are irregularly {948}disposed in the sagittal plane. The ventral rod is strongly curved, often semicircular, the dorsal rod less curved or nearly straight.

_Dimensions_.--Diameter of the gate 0.05 to 0.07; length of the spines 0.004 to 0.02.

_Habitat_.--Cosmopolitan--Atlantic, Pacific; also fossil in Barbados.

11. _Zygocircus bütschlii_, n. sp.

_Zygocircus productus_, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol.
xxxvi. p. 497.

Gate obliquely ovate. Ring irregularly roundish, semi-ovate or ovate, with interrupted and distorted edges, and with a large number (ten to twenty or more) of simple, irregularly formed and asymmetrically disposed spines; commonly some larger spines at the base.

_Dimensions_.--Diameter of the gate 0.05 to 0.09; length of the spines 0.005 to 0.02.

_Habitat_.--Fossil in Barbados.

12. _Zygocircus productus_, Bütschli.

_Zygocircus productus_, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol.
xxxvi p. 496.

_Lithocircus productus_, R. Hertwig, 1879, Organismus d. Radiol., p. 69,
Taf. vii. fig. 4.

Gate obliquely ovate. Ring obliquely ovate, with three complete prominent edges and with numerous (ten to twenty or more) simple, short conical spines, arising in three series from the three edges; commonly some smaller spines at the base.

_Dimensions_.--Diameter of the gate 0.1 to 0.2; length of the spines 0.005 to 0.02.

_Habitat_.--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

Genus 404. _Dendrocircus_,[23] Haeckel, 1881, Prodromus, p. 447.

_Definition_.--#Stephanida# with a simple dipleuric or bilateral ring, armed with branched spines, without typical basal feet.

The genus _Dendrocircus_ has the same dipleuric or bilaterally symmetrical form of the sagittal ring as its ancestral genus _Zygocircus_. It differs from the latter in the development of branched radial spines, and therefore bears to it the same relation as the amphithect _Lithocircus_ does to the simpler _Archicircus_.

1. _Dendrocircus quadrangulus_, n. sp.

Gate irregularly quadrangular or nearly semicircular. Ring quadrangular, edgeless, with four unequal sides; ventral rod more curved and with longer sides than the dorsal rod. From the four edges arise four strong, irregularly branched spines, about as long as the diameter of the gate, {949}with curved branches; the ventral and basal spines larger than the dorsal and apical spines. Similar to _Lithocircus quadricornis_ (Pl. 81, fig. 9), but less branched, and with a striking difference between the shorter dorsal and the longer ventral rod.

_Dimensions._--Diameter of the gate 0.04 to 0.06; length of the spines 0.05 to 0.07.

_Habitat._--North Pacific, Station 256, depth 2950 fathoms.

2. _Dendrocircus dodecarrhiza_, n. sp.

Gate obliquely ovate. Ring irregularly quadrangular, with three prominent edges. From the latter arise at the four corners twelve divergent, irregularly branched spines (three in each corner), about as long as the radius of the gate, with curved branches; the three basal spines larger than the nine others.

_Dimensions._--Diameter of the gate 0.08 to 0.1; length of the spines 0.04 to 0.06.

_Habitat._--Indian Ocean (Maldive Islands), surface (Haeckel).

3. _Dendrocircus dodecancistra_, n. sp. (Pl. 81, fig. 11).

Gate obliquely ovate or nearly elliptical. Ring irregularly ovate, with three distorted edges and six pairs of branched spines. The two ventral pairs are much more distant than the two dorsal pairs, the ventral rod being longer and more curved than the dorsal rod. All twelve spines are of nearly equal size, are more or less curved, about as long as the diameter of the gate, and each bears six to twelve irregular short branches at the end.

_Dimensions._--Diameter of the gate 0.07 to 0.08; length of the spines 0.05 to 0.08.

_Habitat._--Tropical Atlantic, Station 342, depth 1445 fathoms.

4. _Dendrocircus arborescens_, n. sp. (Pl. 81, fig. 10).

Gate irregularly roundish or nearly circular. Ring of the same form, with slight edges and six pairs of elegant arborescent spines (one apical, two dorsal, two ventral, and one basal pair); the three latter somewhat larger than the three former. Each tree is larger than the ring, in the basal half simple, in the distal half forked, each fork-branch with numerous dichotomous terminal branches.

_Dimensions._--Diameter of the gate 0.06 to 0.08; length of the spines 0.12 to 0.15.

_Habitat._--Central Pacific, Stations 266 to 274, surface.

5. _Dendrocircus elegans_, n. sp. (Pl. 81, fig. 13).

Gate irregularly ovate. Ring thick, ovate, with three denticulate edges and six bunches of stout, branched and spinulate, curved spines. The four ventral spines are more distant than the four dorsal, the ventral rod being more curved than the dorsal. The latter bears above the two apical spines. The two basal spines are much larger, deeply forked; their four fork-branches may be compared to the four basal feet of _Stephanium_.

_Dimensions._--Diameter of the ring 0.09 to 0.11; length of the spines 0.03 to 0.06.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

{950}6. _Dendrocircus barbadensis_, n. sp.

Gate irregularly ovate or nearly semicircular. Ring of the same oblique form, thick, with interrupted and distorted edges, armed with eight to twelve larger irregularly formed and branched acute spines; between them numerous conical smaller spines. This common species is very polymorphous and variable.

_Dimensions._--Diameter of the ring 0.05 to 0.08; length of the spines 0.005 to 0.02.

_Habitat._--Fossil in Barbados.

7. _Dendrocircus stalactites_, n. sp. (Pl. 81, fig. 14).

Gate obliquely ovate. Ring irregularly ovate or roundish, very thick, without edges, armed with numerous (eight to twelve or more) short and stout branches, which are shorter than the diameter of the gate, irregularly disposed and branched, with very numerous clustered blunt ramules.

_Dimensions._--Diameter of the gate 0.07 to 0.09; length of the spines 0.02 to 0.06.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Subfamily 2. CORTINIDA, Haeckel.

_Definition._--#Stephanida# with typical basal feet (or cortinar feet).

Genus 405. _Cortina_,[24] n. gen.

_Definition._--#Stephanida# with a simple dipleuric or bilateral ring, bearing at the base three divergent feet (one odd caudal and two paired lateral feet).

The genus _Cortina_ and the following _Stephanium_ represent together the small but very important group of Cortinida, differing from the simple Lithocircida in the possession of three typical basal feet, which are transmitted to the majority of the NASSELLARIA by heredity, and produce their peculiar triradial structure. They appear therefore as a combination of the simple ring (_Zygocircus_) with three basal feet (_Plagonium_). One of these three divergent feet is the odd caudal foot, opposite to the apical horn; the two others are the paired lateral or pectoral feet. (On the probable origin and the typical signification of _Cortina_ compare above, pp. 891-894.)

1. _Cortina tripus_, n. sp. (Pl. 83, fig. 9).

Ring ovate, smooth, or with a few short thorns. Apical horn oblique, curved, simple, smooth, about as long as the sagittal axis of the ring. Feet divergent, curved, simple, smooth, about as {951}long as the horn; the caudal foot shorter than the two pectoral feet. Very variable in form and size.

_Dimensions._--Height of the ring 0.06 to 0.09, breadth 0.04 to 0.06; length of the feet 0.05 to 0.1.

_Habitat._--Cosmopolitan; Atlantic, Indian, Pacific, surface and in various depths.

2. _Cortina typus_, n. sp. (Pl. 97, fig. 1).

Ring kidney-shaped or nearly semicircular, with revolute vertical dorsal rod and strongly curved ventral rod; both rods with two pairs of spine-bunches. Apical horn nearly straight, thorny, longer than the ring, directed a little obliquely backwards. Feet slightly curved, of equal length, two to three times as long as the ring; each armed with few large bunches of curved spines, which are more developed in the caudal foot than in the two pectoral feet.

_Dimensions._--Height of the ring 0.14, breadth 0.08; length of the feet 0.2 to 0.3.

_Habitat._--Tropical Atlantic, Station 348, depth 2450 fathoms.

3. _Cortina conifera_, n. sp.

Ring subcircular, smooth. Apical horn and the three divergent feet of equal size and similar form, cylindrical, straight, about as long as the ring, at the distal end thickened, with a dimply cone (similar to _Tripospyris conifera_ and _Tripospyris eucolpa_, Pl. 84, figs. 4, 7).

_Dimensions._--Height of the ring 0.08, breadth 0.06; length of the feet 0.09.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

4. _Cortina furcata_, n. sp.

Ring elliptical, with three forked horizontal spines (one on the dorsal and two on the ventral rod). Apical horn and the three divergent feet of equal size, somewhat longer than the ring, slightly curved, in the distal half forked.

_Dimensions._--Height of the ring 0.07, breadth 0.05; length of the feet 0.09.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms. Fossil in Barbados.

5. _Cortina dendroides_, n. sp.

Ring ovate, with six pairs of branched horizontal spines, three on the dorsal and three on the ventral rod. Apical horn very large, arborescent, about as long and as broad as the ring. Feet similar to the horn, also richly branched, of equal size. All the rods and their branches curved, with prominent distorted edges.

_Dimensions._--Height of the ring 0.13 to 0.17, breadth 0.1 to 0.12; length of the feet 0.15 to 0.2.

_Habitat._--Central Pacific, Stations 266 to 274, depth 2350 to 2925 fathoms.

{952}6. _Cortina cervina_, n. sp. (Pl. 92, fig. 21).

Ring ovate, with four pairs of forked horizontal spines (two dorsal and two ventral pairs). Apical horn straight and stout, as long as the ring, with trifid point. Three feet equal, widely divergent, very large, branched like a deer's antler, with very numerous short and stout, curved and pointed branches. All rods and branches roundish, without edges.

_Dimensions._--Height of the ring 0.1, breadth 0.07; length of the feet 0.12 to 0.16.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

Genus 406. _Stephanium_,[25] n. gen.

_Definition._--#Stephanida# with a simple dipleuric or bilateral ring, bearing at the base four divergent feet (two sagittal and two lateral feet).

The genus _Stephanium_ differs from the preceding nearly allied _Cortina_ in the production of four basal feet; the new foot, missing in the latter, is the anterior or sternal foot. Therefore _Stephanium_ may be regarded as the archetype of all those NASSELLARIA in which, on the base of the sagittal ring, there are developed four typical feet--two sagittal feet (the posterior caudal and anterior sternal foot) and two lateral feet (right and left). On the origin of _Stephanium_ compare above, p. 893, &c.

1. _Stephanium quadrupes_, n. sp. (Pl. 92, fig. 20).

Ring ovate, with three prominent dentate edges and a short pyramidal apical horn. Four feet all of nearly equal size, about as long as the ring, also with three thorny edges, in the upper half divergent, in the lower convergent.

_Dimensions._--Height of the ring 0.12, breadth 0.08; length of the feet 0.11 to 0.13.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

2. _Stephanium tetrapus_, n. sp.

Ring elliptical, without edges, thorny, with a stout, thorny apical horn of the same length. Four feet curved and irregularly branched, divergent, of different size. The two sagittal feet (the anterior sternal and posterior caudal) about as long as the ring. The two lateral feet (right and left) nearly twice as long, more richly branched.

_Dimensions._--Height of the ring 0.16, breadth 0.11; length of the feet 0.15 to 0.3.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms. Fossil in Barbados.

{953}Family XLIX. #SEMANTIDA#, n. fam.

_Definition._--#Stephoidea# with a single vertical ring (the primary sagittal ring), bearing on its base a horizontal ring (basal or cortinar ring) with two to four or more basal gates (or cortinar pores).

The family #Semantida# differs from the preceding Stephanida in the development of a small horizontal ring on the base of the primary vertical sagittal ring. By the crossing of these two rings a small latticed basal plate is formed, with one or two pairs of pores; rarely with a greater number of "basal pores." The production of this characteristic "basal plate" is of the greatest morphological importance, as the beginning of the numerous different lattice-formations, which are differentiated in the great majority of NASSELLARIA.

In my Prodromus (1881, p. 446) I had enumerated the Semantida with three genera (Nos. 298 to 300) as a separate subfamily of the Dyostephida or "Stephoidea biannularia," and characterised these "Dyostephanida" by the following definition: "Skeleto annulis duobus composito, qui in duobus planis invicem perpendicularibus jacent; altero annulo (sagittali) verticali, altero (basali) horizontali." As the names there given were already employed with another signification, and as the Zygostephanida (there united with the Dyostephanida) are more closely related to the Coronida, I now change the names, and propose to call the family Semantida, expressing by this term the typical similarity of the skeleton to a signet-ring (_Semantis_, _Semantrum_, _Semantidium_).

At about the same time, some #Stephoidea# of this family were accurately described by Bütschli (1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 495, Taf. xxxii. figs. 6, 7, 8). He called them _Stephanolithis_, a name which Ehrenberg had employed, not for complete shells of Radiolaria, but for isolated parts of such, and for siliceous fragments of different skeletons, needles of Sponges, &c. The three species described by Bütschli represent three different genera of our Semantida, viz., _Semantis spinescens_ (with two gates in the basal plate), _Semantrum mülleri_ (with four gates), and _Semantidium haeckelii_ (with six gates). He pointed out the great morphological value of the fenestrated basal plate and its paired gates, as beginnings of numerous other NASSELLARIA. But his opinion, that in all #Spyroidea# and #Cyrtoidea#, derived from these, two pairs of basal gates were constant, was erroneous, nor was the formation of the first pair naturally explained; he supposed that the formation of the basal plate begins by development of an odd sagittal apophysis, arising from the base of the primary sagittal ring. But this odd sagittal apophysis ("der unpaare mediane Kieselfortsatz c1", _loc. cit._, p. 497) is in reality not a primary {954}and essential part of the skeleton, but secondary and of little morphological value, absent in the majority of the Semantida and of the other NASSELLARIA.

We divide our family Semantida into two different subfamilies, which possibly possess a direct phylogenetic relation to the two subfamilies of Stephanida:--The Semantiscida have no typical feet, and have arisen directly from the Lithocircida; the Cortiniscida, however, possess the three typical basal feet of _Cortina_, and may therefore be derived directly from the Cortinida. Since these three cortinar feet are probably identical with the three primary radial rods of the #Plectoidea#, an immediate affinity also to these NASSELLARIA is indicated.

The Semantiscida, which do not possess these three basal cortinar feet, are the simpler forms of the family. The simplest of all, and perhaps the common ancestral form of the whole family, is _Semantis_ (Pl. 92, figs. 1, 2). It may be derived from _Archicircus_ or _Zygocircus_ by development of two pairs of horizontal apophyses on its base, around the porochora of the central capsule. The two rods of each side (right and left), becoming curved one towards the other, and meeting laterally, form a simple horizontal gate, and the two paired basal gates together, a horizontal ring or basal ring, to which the primary sagittal ring is perpendicular. In the next allied genus, _Semantrum_ (Pl. 92, figs. 3-5), three pairs of horizontal apophyses are developed, and therefore two pairs of basal gates produced, an anterior and a posterior. In the third genus, _Semantidium_ (Pl. 92, figs. 6, 7), three pairs of basal pores or gates are visible, surrounded and separated by four pairs of horizontal apophyses, which arise from the base of the sagittal ring. Finally, in _Clathrocircus_ (Pl. 92, figs. 8-10) the number of apophyses is much increased, and two parallel rows of pores are developed along the two sides of the sagittal ring.

The basal plate or the "seal," developed from the base of the primary sagittal ring or "signet-ring," is therefore a horizontal ring, which becomes bisected by the latter, and exhibits either one pair of primary "basal gates" or two or three pairs of these important basal pores, rarely more. Since these pores possess the greatest morphological value, and are probably everywhere homologous, we give to them and to the separating apophyses certain names, and call the anterior pair of gates, "jugular pores" (_i_ in our figures, the pair I of Bütschli); the middle (usually the largest) pair, "cardinal pores" (_k_ in our figures, the pair II of Bütschli), and the posterior, smaller pair, "cervical pores," _l_. The typical pairs of rods, by the union of which these basal pores arise, are the following:--(1) the clavicular or furcular rods, _f_, the first pair (rods _e_1 of Bütschli), (2) the coracal rods, _e_, between the jugular and cardinal pores (rods _e_ of Bütschli), (3) the scapular rods, _g_, between the cardinal and cervical pores (rods _e_2 of Bütschli), (4) the cervical rods, the fourth pair of apophyses, the most posterior, _h_. Bütschli supposes that the topographical succession of the three typical pairs of basal pores is also the chronological succession, the jugular being formed first, the {955}cardinal second and the cervical pores third but it seems that this succession is often altered and that the cardinal pores (the largest), appear first, the jugular pores (in front of them) second and the cervical pores third (or perhaps sometimes in the inverse succession).