Chapter XI: Literature and History (27)

Arms at equal distances, forming a rectangular, regular cross, of the same size and form as the circular central disk, so that the dark interior part of the shell is composed of five equal circular disks, situated in a quincuncial manner. The clearer complete patagium, enveloping the whole cross perfectly, forms a regular square with rounded edges.

_Dimensions._--Radius of the arms 0.2; diameter of each of the five circular disks 0.01; length of the square side 0.35.

_Habitat._--West Indies, Cuba, surface (Thomson).

Subgenus 2. _Spongastromma_, Haeckel.

_Definition._--Cross formed by the four arms bilateral or irregular, with the arms at different distances.

5. _Spongaster orthogonus_, Haeckel.

_Spongocyclia orthogona_, Haeckel, 1862, Monogr. d. Radiol., p. 471, Taf.
xxviii. fig. 3.

_Spongodiscus orthogonus_, Haeckel, 1860, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 844.

Arms at different distances, forming a bilateral cross, grouped in two opposite pairs of equal size and similar form. Arms club-shaped, about as long as the diameter of the central circular disk, enveloped perfectly by the complete patagium, which forms a regular rectangle, the longer side of which is one and a half times as long as the shorter side. (The arms in my figure are not distinctly enough marked.)

_Dimensions._--Radius of the arms 0.08, breadth 0.02; length of the larger side of the rectangle 0.15, of the smaller 0.1.

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

6. _Spongaster scyllaeus_, Haeckel.

_Spongocyclia scyllaea_, Haeckel, 1862, Monogr. d. Radiol., p. 471, Taf.
xxviii. fig. 4.

_Spongodiscus scyllaeus_, Haeckel, 1860, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 844.

Arms at different distances, forming a bilateral cross, grouped in two opposite pairs of different size and form, one pair smaller and less divergent than the other. Arms club-shaped, little longer than the radius of the central circular disk, enveloped perfectly by the complete patagium, which forms a trapezium; the convergent longer sides of the latter are one and a half times as long as the larger, and twice as long as the smaller parallel side. (The arms are in my figure, _loc. cit._, not distinctly enough marked.)

_Dimensions._--Radius of the arms 0.12 to 0.14, breadth 0.02; length of both convergent sides 0.24, of the larger parallel side 0.18, of the smaller 0.12.

_Habitat._--Pacific, central area, Station 272, surface; Mediterranean (Messina).

{599}----

Suborder VI. LARCOIDEA, Haeckel, 1883 (Pls. 9, 10, 49, 50).

_Definition_.--SPUMELLARIA with lentelliptical central capsule (rarely somewhat modified or allomorphic), with a lentelliptical fenestrated siliceous shell (often modified or allomorphic, and sometimes quite irregular). Growth different in the three unequal dimensive axes, perpendicular one to another. The typical Lentellipsis is characterised by three elliptical dimensive planes of different sizes, perpendicular one to another.

The section #Larcoidea#, the fourth and last of the #Sphærellaria#, comprises all those forms of this group in which the fenestrated shell originally is lentelliptical, characterised by different growth in three different axes, perpendicular one to another, all three equal on both poles. The geometrical fundamental form of the shell is therefore a lentellipsis or a triaxial ellipsoid; and this typical form is preserved completely in the majority of #Larcoidea# in the pure geometrical form of the central capsule.

The three dimensive axes, which determine the typical form of #Larcoidea#, are commonly differentiated in such a way, that the first, the longitudinal or principal axis, is the longest; both its poles, oral and aboral (or anterior and posterior) are equal. The second, the lateral or transverse axis, is commonly less than the first, greater than the third axis; both its poles are the equal lateral poles (right and left not differentiated). The third dimensive axis, the equatorial or sagittal axis, is commonly the shortest; both its equal poles are the sagittal poles (dorsal and ventral poles not different). The relative size of the three dimensive axes in the human body exhibits similar relations.

The three dimensive planes of the #Larcoidea#, the sagittal, lateral, and transverse planes, are elliptical, all three of different sizes. The first plane, the median or sagittal plane, is commonly as regards size between the two others; its major axis is the principal, its minor the sagittal axis; it separates the right half of the body from the left. The second plane or lateral plane, is commonly larger than the two others; its major axis the principal, its minor the transverse axis; it separates the dorsal half of the body from the ventral. The third plane, the equatorial or zonal plane, is commonly less than the two others; its major axis the lateral, its minor the sagittal axis; it separates the two principal halves of the body, the oral and aboral halves.

In my Monograph (1862) only very few forms of #Larcoidea# are described, _Tetrapyle_ and _Lithelius_ (the latter representing a peculiar family, Lithelida). In my Prodromus (1881, pp. 463, 464) I disposed all observed forms of #Larcoidea# in two different families, the Pylonida and Lithelida. The rich materials of the Challenger collection have since offered an astonishing number of new and interesting forms of this section, so that I can enumerate here fifty-one genera and two hundred and sixty-five species. I dispose them here in four subsections and nine families. Three of these have regular lentelliptical shells, which are not articulate, and {600}without annular constrictions (Larcarida, Larnacida, Pylonida); these form the subsection Pylolarcida. Two other families (Tholonida and Zonarida) are distinguished by annular constrictions, which divide the regular lentelliptical shell into a number of dome-shaped chambers or cupolas; we call these Thololarcida. A third group, Spirolarcida, comprises the #Larcoidea# with spiral growth; the two families of Lithelida and Streblemida. Finally a fourth group the Sorolarcida is formed by the #Larcoidea# with irregular shells, also two families, the Phorticida and Soreumida.

The first family of #Larcoidea#, the Larcarida, contains the most simple forms, beginning with _Cenolarcus_, a quite simple lentelliptical latticed shell. In _Coccolarcus_ we find already two concentric shells, connected by radial beams, an inner medullary and an outer cortical shell. In _Spongolarcus_ the lentelliptical shell becomes spongy.

The second family, Larnacida, is very similar to the Larcarida, and seems to diverge only by the different mode of connection between the two concentric lentelliptical shells. But in truth this slight difference is of great morphological importance, as it depends on a quite different and peculiar mode of growth. In the foregoing Larcarida (_Coccolarcus_, &c.), the concentric shells originate in the same manner as in the concentric #Prunoidea# and #Sphæroidea#, by radial beams, which arise from the surface of the inner (medullary) shell and become connected by a network to form the outer (cortical) shell. Here, in the Larnacida, a quite similar shell originates in a quite different way, first arrived at in the Pylonida (_Trizonium_). Both concentric shells become here connected by peculiar lattice girdles, which are developed in the perimeter of the three elliptical dimensive planes. Firstly, on both sides of a simple, spherical, or lentelliptical central chamber, arise two lateral wings (on the poles of the transverse axis), and build around the former a transverse girdle. This is crossed by a larger lateral girdle, the minor axis of which is the major of the former, and perpendicular to both girdles is yet developed a third, the sagittal girdle. If the open fissures or "gates" between these three girdles become closed by network, we obtain _Larnacilla_, the probable ancestral form of all Larnacida.

Whilst in _Larnacilla_ and _Larnacidium_ this typical trizonal lentelliptical shell constitutes by itself alone the whole skeleton, in the other Larnacida it becomes overgrown by outer envelops, and so becomes enclosed in the interior of the central capsule as a "_Larnacilla_-shaped medullary shell." If the enclosing external envelops be simply latticed, we get the subfamily Larnacalpida; if they be spongy, we get the Larnacospongida.

The third family, Pylonida, is the most important of all #Larcoidea#, as not only the largest and most interesting number of species belong to it, but also many other genera (far the greater part of all #Larcoidea#) may be derived from it. The peculiar character of the Pylonida is determined by the imperfect fenestration of the lentelliptical shell growing in the three dimensive axes in a quite different manner. Each elliptical dimensive plane becomes circumscribed by an elliptical latticed girdle (or fenestrated {601}ring), and between these three girdles (perpendicular one to another) remain wide open fissures of the shell or "gates" (_Pylæ_). The beginning of the shell-building is the same as in _Larnacilla_, the most simple form of Larnacida. From a quite simple medullary shell, a spherical, subspherical, ellipsoidal, or lentelliptical central chamber, arise two latticed wings, opposite on the poles of the transverse axis (_Monozonium_). Both wings are short and wide hollow fenestrated tubes, the axes of which are parallel to the principal axis. Therefore they form together with the central chamber an elliptical transverse girdle. This first girdle becomes crossed by a second lateral girdle; from both poles of the transverse axis arise latticed wings, which unite on the poles of the principal axis, therefore the minor axis of this second larger ring is the major axis of the first smaller ring (_Dizonium_). Between the two crossed rings remain four wide open gates. Now follows the development of a third sagittal girdle, arising from both poles of the principal axis and overgrowing the four gates. But as this third girdle is larger than the second, four other larger gates arise between the two (in planes perpendicular to the former four gates). Now we have the characteristic and most important trizonal shell (_Trizonium_), composed of three elliptical lattice-girdles of different size, perpendicular one to another, and enclosing a simple central chamber. If the four gates of this _Trizonium_ become closed by lattice-work, it passes over into _Larnacilla_, the most important ancestral form of the Larnacida.

This most significant "trizonal shell," either incompletely latticed in _Trizonium_ (with four open gates), or completely latticed by fenestration of the four gates, in _Larnacilla_, is to be found in far the greater part of all #Larcoidea#, representing the medullary shell, which is overgrown by an outer cortical shell. In many #Larcoidea#, in which this "_Larnacilla_-shell" is absent, it is perhaps lost by phylogenetic reduction, or retrograde metamorphosis.

The same process of triple girdle-building, by which the typical _Trizonium_-shell or _Larnacilla_-shell is produced (Haplozonaria), is repeated once or twice in the larger forms of Pylonida. The first system of three girdles (perpendicular one to another) becomes overgrown by a second system of the same formulation in the Diplozonaria, and this becomes overgrown by a third system in the Triplozonaria; in the highest genus of this group, _Pylozonium_, we find not less than nine girdles (three systems, each of three girdles). Till now only one genus of the whole polymorphous family was well known, _Tetrapyle_ (with five girdles, three of the medullary, two of the cortical shell). If the gates between the girdles remain open, all these forms must be regarded as Pylonida; if the gates afterwards become closed by a network, they pass over into other families.

The fourth family of the _Larcoidea_ is the Tholonida, distinguished by the polythalamous shell being composed of a certain number of roundish or hemispherical chambers (domes or cupolas), which surround a primordial central chamber in quite regular disposition, lying opposite in pairs on the poles of the three dimensive axes. {602}If we imagine that each "wing" (or open half-girdle) of the Pylonida becomes closed by a lattice-work, and so transformed into a hemispherical or roundish cupola, we obtain the characteristic shell of the Tholonida. Indeed every girdle of the former corresponds to a pair of opposite domes of the latter. The axis of each pair of domes is one of the three dimensive axes.

The primordial chamber of the Tholonida (or the central chamber, around which all cupolas are regularly disposed) is either a simple lentelliptical lattice-shell, like _Cenolarcus_, or it is a trizonal shell (with an enclosed concentric medullary shell), like _Larnacilla_. As in both cases the building and the disposition of the cupolas around it are quite the same, we can suppose that the whole family of Tholonida may have been derived originally from _Larnacilla_ (or _Trizonium_), and that the Cenotholida (with a simple central chamber) are sprung from the Coccotholida (with a _Larnacilla_-shaped central chamber) by reduction and loss of the original medullary shell.

The family Tholonida can be divided into three subfamilies according to the disposition of the cupola-pairs in one, two, or three dimensive axes. In the Cubotholida lie two cupolas on the poles of the transverse axis of the central chamber (corresponding to _Amphipyle_); in the Staurotholida we find four cupolas crosswise disposed, on the poles of the transverse and principal axes (corresponding to _Tetrapyle_); in the Cubotholida are at least six cupolas, on the poles of all three dimensive axes (corresponding to _Tholonium_). In all three cases the number of cupolas may be augmented by the secondary apposition of other chambers or domes in the same disposition. Sometimes also the whole cortical shell becomes enclosed by an external veil or mantle of delicate network. The lentelliptical (or often nearly cubical) central chamber becomes often reduced, so that its sides are incompletely latticed or widely opened; in some Cubotholida only the twelve edges of the eight cornered cubical central chamber remain; its six sides are quite open and only over-vaulted by the six hemispherical cupolas. From the opposite points of the latter (in the deep annular constrictions between them) often arise radial spines, and these lie commonly in diagonal planes, separating the dome-pairs.

A similar dome-building or a composition of the polythalamous shell by pairs of cupolas we find also in the next (fifth) family, the Zonarida. But here the true cause of the peculiar dome-structure is quite different, not an apposition of new chambers, but the constriction of a cortical shell-like _Larnacalpis_ by two or more constrictions. These constrictions lie in dimensive planes (or in planes parallel to these), and therefore the cupolas are (all or partly) in diagonal planes, a condition quite opposite to that found in the Tholonida. One of the annular constrictions is constantly in the sagittal plane (separating the right and left halves of the shell). The number of the constrictions in the few genera is two, three, and four, and therefore the number of the cupolas four, six, or eight. As this cortical shell constantly encloses a trizonal medullary shell (or _Larnacilla_-shell), we cannot doubt that the Zonarida must be derived from the Larnacida.

{603}Whilst in all the foregoing five families of #Larcoidea# the shell-form is regular and their geometrical fundamental form is a lentellipsis (or a triaxial ellipsoid, with three unequal isopolar dimensive axes), in the four remaining families of this suborder the shell becomes bilateral or irregular (with the poles of the axes unequal). In two of these families (Lithelida and Streblemida) the growth of the shell becomes spiral, in the last two families (Soreumida and Phorticida) quite irregular. But as in all four families we encounter the typical trizonal medullary shell (or _Larnacilla_-shell), we are convinced that they must be derived (wholly or partially) from the Larnacida.

The Lithelida (the sixth family) are #Larcoidea# with spiral growth and bilateral form (like _Nautilus_); therefore the spiral line lies in one plane and this spiral plane divides the whole shell into two symmetrical halves (right and left). The axis of the spiral (around which the shell winds) is a straight line, one of the three dimensive axes. In the greater part of Lithelida (in the Larcospirida) the primordial of central chamber of the polythalamous shell is a trizonal medullary shell or _Larnacilla_-shell, and the growth of the first spiral turning begins as the development of the first (transverse) cortical girdle of _Amphipyle_; but as one wing (or lateral half) of this girdle grows more rapidly than the other, it overgrows the latter and begins the spiral winding; if the other wing follow and overgrow the first, the spiral becomes double. Each of the three dimensive girdles (of the Pylonida) may begin the spiral winding. There can be no doubt that all these Lithelida (the Larcospirida) must be derived from the Pylonida, by unequal growth of the two halves of one girdle. Perhaps from these may also derived the other part of this family, the Spiremida (_Spirema_ and _Lithelius_); in these the primordial chamber of the spiral shell is simple, and may be derived by reduction of the original _Larnacilla_-shell. But it is also possible that the Spiremida proceed directly from the Larcarida, and that their ancestors did not possess a _Larnacilla_-shell.

The Streblemida (the seventh family) are #Larcoidea# with spiral growth and asymmetrical form of the polythalamous shell (like _Helix_ or _Turrilites_); therefore the spiral line is twisted like a winding stair, and the spiral face is curved and divides the shell into two unequal halves. The Streblemida have the same likeness and relation to the turbinoid Foraminifera (_Rotalia_, _Globigerina_, &c.) as the Lithelida to the nautiloid Foraminifera (_Polystomella_, _Nummulina_, &c.). As in these calcareous Rhizopods also the peculiar growth of the siliceous Streblemida begins from a primordial chamber to which a variable number of roundish chambers (of increasing size) is apposed. But the building of these chambers and of their septa is by no means so regular and complete as in the greater number of turbinoid Foraminifera. As in a part of this family the primordial chamber is _Larnacilla_-shell, these also may be derived from the Larnacida, but the other part (with simple central chamber) is perhaps produced directly from the Larcarida.

The eighth family, Soreumida, is perhaps derived from the Streblemida by the loss of the spiral growth. The polythalamous shell is similar to the latter, but the chambers are {604}aggregated without any order, like the Acervulinida among the Foraminifera. In some cases also here the primordial chamber is a trizonal _Larnacilla_-shell, in other cases it is a simple, subspherical or lentelliptical shell.

The last family, the Phorticida, is formed of irregular #Larcoidea#, in which a lentelliptical trizonal _Larnacilla_-shell (as an inner medullary shell) is enveloped by an irregular, latticed, or spongy cortical shell. They can be regarded as abnormalities or irregular deformities of Larnacida or Pylonida.

The central capsule of the #Larcoidea# is originally lentelliptical and preserves this form, the "triaxial ellipsoid," in the greater number of genera. In some groups it follows the prevalent growth of the shell in the direction of one of the three dimensive axes, and becomes prolonged in this way. In many chambered forms (particularly Tholonida and Zonarida) the growing central capsule gets constricted, corresponding to the constrictions of the shell. In the Soreumida and Phorticida its form often becomes irregular. But in general for the greater number of #Larcoidea# the lentelliptical form of their central capsule is quite characteristic.

_Synopsis of the Families of_ #Larcoidea#.

-------------------------------------------------------------------------
#Larcoidea# with a regular or symmetrical shell, the growth of which is
determined by the three dimensive axes. (Both poles of each axis are
equal.)
-------------------------------------------------------------------------
{Medullary shell absent or
Cortical shell completely { simple (spherical or
latticed, without external { lentelliptical), 1. LARCARIDA.
gates (or interzonal {
fissures), without annular {Medullary shell trizonal or
constrictions and domes. { _Larnacilla_-shaped
{ (composed of three
{ dimensive girdles), 2. LARNACIDA.

Cortical shell incompletely latticed, with two to four or
more symmetrically disposed gates or fissures remaining
between latticed dimensive girdles, 3. PYLONIDA.

Cortical shell completely }Constrictions of the
latticed, without external } cortical shell in
gates (or interzonal } diagonal planes; domes
fissures), with two or } in dimensive axes, 4. THOLONIDA.
more annular constrictions,}
which separate three to }Constrictions of the
six or more dome-shaped } cortical shell in
protuberances. } dimensive planes; domes
} in diagonal axes, 5. ZONARIDA.
-------------------------------------------------------------------------
#Larcoidea# with a symmetrical or irregular shell, either with
spiral growth or with quite irregular growth. (Both poles of one axis
are different.)
-------------------------------------------------------------------------
{Spiral cortical shell bilateral
{ (with plane spiral), 6. LITHELIDA.
Cortical shell with {
spiral growth. {Spiral cortical shell
{ asymmetrical (with ascending
{ spiral), 7. STREBLEMIDA.

{Cortical shell simple, with
{ one single chamber, 8. PHORTICIDA.
Cortical shell with quite {
irregular growth. {Cortical shell composed of
{ a number of heaped up
{ or aggregated chambers, 9. SOREUMIDA.

{605}Family XXIV. #LARCARIDA#, Haeckel, 1883 (Pl. 50, figs. 1, 2).

_Definition._--#Larcoidea# with a regular, completely latticed, lentelliptical cortical shell, without open gates and annular constrictions; medullary shell absent or simple (not trizonal), connected with the cortical shell by radial beams.

The family #Larcarida# opens the long series of #Larcoidea# as the most simple group of this suborder. It commences with _Cenolarcus_, a quite simple lentelliptical latticed shell, which is characterised by three unequal isopolar dimensive axes, perpendicular one to another. The major of these three axes is the longitudinal or principal, the middle is the lateral or transverse, and the minor is the equatorial or sagittal axis (as in the human body). Among the three dimensive planes, which are determined by pairs of these axes, the lateral plane is the largest (halved by the crossed principal and lateral axes). The intermediate is the sagittal plane or median plane (halved by the crossed principal and sagittal axes). The smallest is the equatorial plane or transverse plane (halved by the crossed lateral and sagittal axes). Therefore the shell has all the characters of the true _Lentellipsis_ or of the "triaxial ellipsoid," and its axes agree with the three axes of the "rhombic crystalline system."

In the three subfamilies of Larcarida this lentelliptical shell assumes a different shape: in the Cenolarcida it remains simple, in the Spongolarcida it becomes spongy (sometimes quite filled out with a spongy framework), in the Coccolarcida it is composed of two or more concentric lentelliptical shells (at least an inner medullary and one outer cortical shell). These shells are simply connected by radial beams, and not, as in the Larnacida, by latticed wings (or half girdles).

The network of the Larcarida shell is sometimes regular, commonly irregular (as in the greater number of #Larcoidea#). The surface of the shell is sometimes smooth or thorny, at other times covered with radial spines. These are often symmetrically disposed, either on the poles of the dimensive axes or in crossed diagonal planes.

The central capsule is a true "lentellipsis" in a geometrical sense; it is halved by three elliptical dimensive planes of different sizes, perpendicular one to another. In the Cenolarcida the central capsule lies freely inside the simple (cortical) shell, only separated from it by the jelly-mantle. In the Coccolarcida it contains the medullary shell, and is enclosed by the simple or double cortical shell, perforated by the radial beams connecting the two shells. The spongy shell of the Spongolarcida exhibits a different relation to the central capsule: in _Spongolarcus_ the latter lies freely in the internal cavity of the spongy shell; in _Stypolarcus_, where this cavity is quite filled with a spongy network, the central capsule also contains a part of it.

The morphological and phylogenetic relations of the Larcarida to the other families of SPUMELLARIA admit of a different explanation. As this family contains the {606}most simple forms of all #Larcoidea#, we can regard the _Cenolarcus_ as the common ancestral form of this group, having originated from _Actilarcus_ (or the lentelliptical _Actissa_) by the building of a simple lentelliptical lattice-shell. But it is also possible that a part of the Larcarida (or all?) descend from Larnacida by reduction or loss of the original _Larnacilla_-shell (compare _Cenolarcus triaxonius_, p. 607).

_Synopsis of the Genera of the Larcarida._

-------------------------------------------------------------------------
I. Subfamily Cenolarcida.
Shell simple, latticed (lentelliptical cortical shell).
-------------------------------------------------------------------------
Without radial spines, 266. _Cenolarcus_.

With radial spines, 267. _Larcarium_.
-------------------------------------------------------------------------
II. Subfamily Coccolarcida.
Shell composed of two or more concentric latticed shells (inner
medullary and outer cortical).
-------------------------------------------------------------------------
Without radial spines, 268. _Coccolarcus_.

With radial spines, 269. _Larcidium_.
-------------------------------------------------------------------------
III. Subfamily Spongolarcida.
Shell spongy, partly or whole composed of a spongy framework.
-------------------------------------------------------------------------
With an internal cavity, 270. _Spongolarcus_.

Without an internal cavity, 271. _Stypolarcus_.

Subfamily 1. CENOLARCIDA, Haeckel.

_Definition._--#Larcarida# with a simple, lentelliptical latticed shell (cortical shell without a medullary shell).

Genus 266. _Cenolarcus_,[305] n. gen.

_Definition._--#Larcarida# with a simple, lentelliptical latticed shell, without a medullary shell, without radial spines.

The genus _Cenolarcus_ begins the group of #Larcoidea# as the most simple form of this suborder. It corresponds to _Cenosphæra_ among the #Sphæroidea#, to _Cenodiscus_ among the #Discoidea#, to _Cenellipsis_ among the #Prunoidea#. The simple latticed shell is distinguished from that of the three other genera by its typical lentelliptical form, a triaxial ellipsoid with three dimensive axes of unequal length. Probably _Cenolarcus_ is the original ancestral form of the #Larcoidea#, derived from _Actilarcus_ (the lentelliptical _Actissa_) by the formation of a simple fenestrated shell around the lentelliptical central capsule. But possibly also some species of _Cenolarcus_ may be derived from _Coccolarcus_ or _Larnacilla_ by reduction and loss of the medullary shell (compare _Cenolarcus triaxonius_, n. sp.).

{607}1. _Cenolarcus primordialis_, n. sp. (Pl. 50, figs. 7, 7_a_, 7_b_).

Network of the shell regular, with circular, hexagonally framed pores, twice as broad as the elevated bars; about ten pores on the half meridian, eight on the half equator. Surface a little rough. Proportion of the three dimensive axes = 2 : 2.5 : 3.

_Dimensions._--Principal axis (or length) 0.12, transverse axis (or breadth) 0.1, sagittal axis (or thickness) 0.08; pores 0.01, bars 0.005.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

2. _Cenolarcus dimensivus_, n. sp.

Network of the shell regular, with circular pores (without hexagonal frames), three times as broad as the thin bars; about twelve pores on the half meridian, nine on the half equator. Surface thorny. Proportion of the three dimensive axes = 3 : 4 : 5.

_Dimensions._--Principal axis 0.15, transverse axis 0.12, sagittal axis 0.09; pores 0.012, bars 0.004.

_Habitat._--North Pacific, Station 244, surface.

3. _Cenolarcus triaxonius_, n. sp.

Network of the shell regular, with circular, hexagonally framed pores, four times as broad as the thin bars; about twelve pores on the half meridian, nine on the equator. Surface smooth. From the inner surface of the shell arise six very thin radial beams, opposite in pairs in the three dimensive axes; all six beams end freely in a little knob, at an equal distance from the centre; therefore this remarkable species seems to have lost a medullary shell (descending from _Coccolarcus_ or _Larnacilla_?). Proportion of the three dimensive axes = 2 : 2.5 : 3.

_Dimensions._--Principal axis 0.13, transverse axis 0.11, sagittal axis 0.09; pores 0.012, bars 0.03.

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

4. _Cenolarcus lentellipticus_, n. sp.

Network of the shell regular, with circular pores of the same breadth as the thick bars; about eighteen pores on the half meridian, fourteen on the half equator. Surface smooth. Proportion of the three dimensive axes = 2 : 3 : 4.

_Dimensions._--Principal axis 0.16, transverse axis 0.12, sagittal axis 0.08; pores and bars 0.004.

_Habitat._--Western Tropical Pacific, Station 224, surface.

5. _Cenolarcus minimus_, n. sp.

Network of the shell subregular, with very small circular pores of the same breadth as the bars; only four pores on the half meridian, three on the half equator. Surface smooth. Proportion of the three dimensive axes = 3 : 4 : 5.

{608}_Dimensions._--Principal axis 0.05, transverse 0.04, sagittal axis 0.03; pores and bars 0.006.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

Genus 267. _Larcarium_,[306] n. gen.

_Definition._--#Larcarida# with a simple, lentelliptical latticed shell, without a medullary shell; surface covered with radial spines.

The genus _Larcarium_ differs from _Cenolarcus_ only in the possession of radial spines on the surface of the simple fenestrated lentelliptical shell. These spines are commonly disposed symmetrically, opposite in pairs, either on the poles of the three dimensive axes, or on the poles of certain diagonal axes. Larcarium differs from the similar genera _Larcidium_, _Larnacidium_, and _Larnacantha_ by the absence of any medullary shell.

1. _Larcarium amphistylum_, n. sp.

Shell thorny, with two large conical spines, opposite on both poles of the principal axis, somewhat longer than it. Network of the shell regular, with circular, hexagonally framed pores, twice as broad as the bars; about twelve pores on the half meridian, ten on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5.

_Dimensions._--Principal axis (or length) 0.15, transverse axis (or breadth) 0.12, sagittal axis (or thickness) 0.09; pores 0.01, bars 0.005.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

2. _Larcarium staurostylum_, n. sp.

Shell smooth, with four short three-sided pyramidal spines of equal length, opposite in pairs on the poles of the principal and lateral axes. Network of the shell regular, with circular pores of the same breadth as the bars; about eight pores on the half meridian, six on the half equator. Proportion of the three dimensive axes = 2 : 2.5 : 3.

_Dimensions._--Length of the shell 0.12, breadth 0.1, thickness 0.08; pores and bars 0.006.

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

3. _Larcarium hexastylum_, n. sp.

Shell smooth, with six short conical spines of equal length (= the shortest axis of the shell), opposite in pairs on the poles of the three dimensive axes. Network of the shell subregular, with {609}circular pores three times as broad as the bars; about eleven pores on the half meridian, nine on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5.

_Dimensions._--Length of the shell 0.1, breadth 0.08, thickness 0.06, pores 0.006; bars 0.002.

_Habitat._--North Pacific, Station 244, surface.

4. _Larcarium axostylum_, n. sp.

Shell thorny, with six strong conical radial spines, opposite in pairs on the poles of the three dimensive axes. All three pairs are of different sizes, the length of each spine corresponding nearly to the size of the shell-axis, of which it is the prolongation. Network of the shell subregular, with circular pores twice as broad as the bars; ten on the half meridian, eight on the half equator. Proportion of the three dimensive axes = 2 : 3 : 4.

_Dimensions._--Length of the shell 0.12, breadth 0.09, thickness 0.06; pores 0.01, bars 0.005.

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

5. _Larcarium octostylum_, n. sp.

Shell thorny, with eight thin cylindrical radial spines, opposite in pairs in two crossed diagonal planes. Network of the shell irregular, with roundish pores, twice to four times as broad as the bars; nine to eleven on the half meridian, five to seven on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5.

_Dimensions._--Length of the shell 0.11, breadth 0.09, thickness 0.07; pores 0.006 to 0.012, bars 0.003.

_Habitat._--Pacific, central area, Station 267, surface.

6. _Larcarium polystylum_, n. sp.

Shell thorny, with numerous (twenty to thirty) stronger conical radial spines, about as long as the shortest axis of the shell. Network of the shell irregular, with roundish pores, twice to four times as broad as the bars; seven to eight on the half meridian, five to six on the half equator. Proportion of the three dimensive axes = 1 : 2 : 3.

_Dimensions._--Length of the shell 0.09, breadth 0.06, thickness 0.03; pores 0.006 to 0.012, bars 0.003.

_Habitat._--South Atlantic, Station 323, surface.

7. _Larcarium chætostylum_, n. sp.

Shell bristly, with very numerous (sixty to eighty or more) very thin, bristle-like, radial spines, somewhat longer than the longest axis of the shell. Network irregular, with very small roundish pores, about the same size as the bars; sixteen to eighteen on the half meridian, thirteen to fifteen on the half equator. Proportion of the three dimensive axes = 1 : 1.5 : 2.

{610}_Dimensions._--Length of the shell (without spines) 0.13, breadth 0.1, thickness 0.07; pores and bars 0.004 to 0.006.

_Habitat._--Pacific, central area, Station 273, surface.

Subfamily 2. COCCOLARCIDA, Haeckel.

_Definition._--#Larcarida# with encased lentelliptical shell, composed of two or more concentric lentelliptical latticed shells, which are united by radial beams (at least one inner medullary shell and one outer cortical shell).

Genus 268. _Coccolarcus_,[307] n. gen.

_Definition._--#Larcarida# with two concentric latticed shells, an outer lentelliptical cortical shell, and an inner (spherical or lentelliptical) medullary shell, both connected by radial beams. Surface without radial spines.

The genus _Coccolarcus_ differs from _Cenolarcus_ by the possession of an internal medullary shell. This is quite simple, either spherical or lentelliptical, and connected with the outer cortical shell by a number of radial beams. In the similar _Larnacilla_ this connection is effected by four internal latticed lamellæ (the half lateral wings of the transverse girdle); therefore we find here four internal gates (on the poles of the principal axis), absent in _Coccolarcus_.

1. _Coccolarcus lentellipsis_, n. sp.

Cortical shell with smooth surface and regular network; pores circular, twice as broad as the bars; about thirteen on the half meridian, eleven on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5. Medullary shell spherical, half as broad as the transverse radius.

_Dimensions._--Principal axis (or length) of the cortical shell 0.15, transverse axis (or breadth) 0.12, sagittal axis (or thickness) 0.09; pores 0.01, bars 0.005; diameter of the medullary shell 0.03.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

2. _Coccolarcus platellipsis_, n. sp.

Cortical shell with thorny surface and irregular network; pores roundish, twice to three times as broad as the bars; sixteen to eighteen on the half meridian, ten to twelve on the half equator. Proportion of the three dimensive axes = 1 : 2 : 3. Medullary shell lentelliptical, one-third as large as the cortical shell.

{611}_Dimensions._--Length of the cortical shell 0.17, breadth 0.11, thickness 0.06; pores 0.008 to 0.012, bars 0.004; medullary shell 0.03 to 0.06.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

Genus 269. _Larcidium_,[308] n. gen.

_Definition._--#Larcarida# with two concentric latticed shells, an outer lentelliptical cortical shell, and an inner (spherical or lentelliptical) medullary shell, both connected by radial beams. Surface covered with radial spines.

The genus _Larcidium_ differs from the foregoing _Coccolarcus_ only in the possession of radial spines, and bears to it the same relation that _Larcarium_ does to _Cenolarcus_. The spines are commonly symmetrically disposed, opposite in pairs in the dimensive axes, sometimes also in diagonal axes.

1. _Larcidium dissacanthum_, n. sp.

Cortical shell with thorny surface and regular network; pores circular, hexagonally framed, three times as broad as the bars; about thirteen on the half meridian, eleven on the half equator. Proportion of the three dimensive axes = 2 : 3 : 5. Medullary shell spherical, one-fourth as broad as the cortical, connected with it by two thin beams, lying in the principal axis, and prolonged on its poles into two strong conical spines, somewhat longer than the greatest axis.

_Dimensions._--Length of the cortical shell (or principal axis) 0.15, breadth 0.09, thickness 0.07; pores 0.015, bars 0.005; medullary shell 0.025.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

2. _Larcidium hexacanthum_, n. sp.

Cortical shell with smooth surface and regular network; pores circular, twice as broad as the bars; about eleven on the half meridian, nine on the half equator. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell spherical, one-third as broad as the cortical. On the surface six strong, three-sided pyramidal spines, all about as long as the breadth of the cortical shell.

_Dimensions._--Length of the cortical shell 0.12, breadth 0.1, thickness 0.08; pores 0.01, bars 0.005; medullary shell 0.035.

_Habitat._--Pacific, central area. Station 266, surface.

3. _Larcidium axacanthum_, n. sp.

Cortical shell with rough surface and irregular network; pores roundish, twice to four times as broad as the bars; about fifteen to nineteen on the half meridian, twelve to fourteen on the half {612}equator. Proportion of the three axes = 2 : 3 : 4. Medullary shell lentelliptical, of the same form and structure as the cortical, but only one-third as large, connected with it by six thin radial beams, lying in pairs in the three dimensive axes; on the outside they are prolonged into six strong conical radial spines, which are in pairs of different size (as in _Larcarium axostylum_); the length of each spine nearly equals the axis of the cortical shell, of which it is the prolongation.

_Dimensions._--Length of the cortical shell (and the principal spines) 0.18, breadth of it (and length of the lateral spines) 0.135, thickness of it (and length of the sagittal spines) 0.09; pores 0.005 to 0.013, bars 0.003.

_Habitat._--Pacific, central area, Station 271, surface.

4. _Larcidium octacanthum_, n. sp.

Cortical shell thorny, with irregular network; pores roundish, once to four times as broad as the bars; about thirteen to fifteen on the half meridian, eleven to thirteen on the half equator. Proportion of the three axes = 1 : 2.5 : 4. Medullary shell lentelliptical, one-fifth as large as the cortical, connected with it by eight radial beams, which are situated in two crossed diagonal planes (opposite in pairs), and are prolonged on the surface into eight long and thin cylindrical radial spines similar to _Tetrapyle octacantha_.

_Dimensions._--Length of the cortical shell 0.16, breadth 0.11, thickness 0.045; pores 0.003 to 0.012, bars 0.003; medullary shell 0.02 to 0.03.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

5. _Larcidium dodecanthum_, n. sp. (Pl. 50, figs. 8, 8_a_).

Cortical shell rough, with irregular network; pores roundish, twice to four times as broad as the bars; about twelve to fourteen on the half meridian, eight to ten on the half equator. Proportion of the three axes = 2 : 3 : 4. Medullary shell lentelliptical, one-third as large as the cortical, connected with it by twelve thin radial beams, which are prolonged outside into twelve strong conical radial spines, about half as long as the breadth of the shell.

_Dimensions._--Length of the cortical shell 0.14, breadth 0.1, thickness 0.07; pores 0.008 to 0.015, bars 0.004; medullary shell 0.04 to 0.05.

_Habitat._--South Pacific, Station 288, surface.

6. _Larcidium polyacanthum_, n. sp.

Cortical shell spiny, with irregular network; pores roundish, once to twice as broad as the bars; about ten to twelve on the half meridian, six to eight on the half equator. Proportion of the three axes = 1 : 2 : 3. Medullary shell lentelliptical, half as large as the cortical shell, connected with it by numerous (twenty to twenty-five) radial beams, which are prolonged outside into three-sided pyramidal spines, about as long as the breadth of the shell.

_Dimensions._--Length of the cortical shell 0.18, breadth 0.12, thickness 0.06; pores 0.01 to 0.015, bars 0.008; medullary shell 0.03 to 0.09.

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

{613}Subfamily 3. SPONGOLARCIDA, Haeckel.

_Definition._--#Larcarida# with spongy lentelliptical shell (with or without enclosed medullary shell).

Genus 270. _Spongolarcus_,[309] n. gen.

_Definition._--#Larcarida# with lentelliptical spongy shell, containing a central cavity of the same form, without medullary shell (without radial spines).

The genus _Spongolarcus_ differs from _Cenolarcus_ (its probable ancestral form) only in the development of spongy framework forming the wall of the hollow lentelliptical shell. It corresponds, therefore, to _Plegmosphæra_ among the #Sphæroidea#, and to _Spongellipsis_ among the #Prunoidea#. From these two similar spongy #Sphærellaria# it differs in its characteristic lentelliptical form, with three dimensive axes of unequal length.

1. _Spongolarcus lentellipsis_, n. sp.

Spongy network of the shell very loose, its meshes fifteen to twenty times as broad as the bars. Surface of the shell nearly smooth; diameter of its internal cavity twice as large as the thickness of its wall. Proportion of the three dimensive axes = 2 : 3 : 4.

_Dimensions._--Length 0.16, breadth 0.12, height 0.08; thickness of the spongy wall 0.05.

_Habitat._--Pacific, central area, Station 274, surface.

2. _Spongolarcus triaxonius_, n. sp.

Spongy network of the shell rather loose, its meshes twelve to sixteen times as broad as the bars. Surface of the shell rough; diameter of its internal cavity about eight times as large as the thickness of its wall. Proportion of the three dimensive axes = 2 : 2.5 : 3.

_Dimensions._--Length 0.25, breadth 0.2, height 0.16; thickness of the spongy wall 0.025.

_Habitat._--North Pacific, Station 253, surface.

3. _Spongolarcus dimensivus_, n. sp.

Spongy network of the shell dense, its meshes four to eight times as broad as the bars. Surface of the shell thorny; diameter of its internal cavity about fifteen times as large as the thickness of its wall. Proportion of the three dimensive axes = 3 : 4 : 5.

_Dimensions._--Length 0.2, breadth 0.16, height 0.12; thickness of the spongy wall 0.01.

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

{614}4. _Spongolarcus amphicentria_, Haeckel.

? _Amphicentria salpa_, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 296; Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, Taf.
ii. fig. 18.

? _Spongurus salpa_, Haeckel, 1862, Monogr. d. Radiol., p. 466.

Spongy network of the shell compact, its meshes about the same breadth as the bars. Surface of the shell spiny, with some larger spines around the poles of the axis; diameter of the internal cavity about six times as large as the thickness of its wall. Proportion of the three dimensive axes = 1 : 2 : 3. (Perhaps this _Spongolarcus_ is identical with _Amphicentria salpa_, very imperfectly described and figured by Ehrenberg, _loc. cit._?)

_Dimensions._--Length 0.14, breadth 0.09, height 0.05; thickness of the spongy wall 0.015.

_Habitat._--North Atlantic; off Greenland, 1000 fathoms, Ehrenberg; Station 64, depth (2700) fathoms.

Genus 271. _Stypolarcus_,[310] n. gen.

_Definition._--#Larcarida# with lentelliptical spongy shell, composed of compact spongy framework, without central cavity and medullary shell (without radial spines).

The genus _Stypolarcus_ differs from _Spongolarcus_ in the absence of any central cavity. This is quite filled up by spongy framework, which forms the whole mass of the lentelliptical body. _Stypolarcus_ bears therefore the same relation to _Spongolarcus_ that _Styptosphæra_ does to _Plegmosphæra_.

1. _Stypolarcus spongiosus_, n. sp.

Lentelliptical shell composed in the whole mass of loose, spongy framework of similar texture, with irregular meshes, about ten to twenty times as broad as the thin bars. Surface rough, without radial spines. Proportion of the three axes = 3 : 4 : 5.

_Dimensions._--Length 0.2, breadth 0.16, height 0.12.

_Habitat._--Antarctic Ocean, Station 157, depth 1950 fathoms.

Family XXV. #LARNACIDA#, Haeckel, 1883 (Pl. 50, figs. 3-8).

_Definition._--#Larcoidea# with a regular, completely latticed, lentelliptical cortical shell, without open gates and annular constrictions; either this cortical shell or the enclosed medullary shell is trizonal, composed of three elliptical, latticed, dimensive girdles of different sizes, perpendicular one to another.

{615}The family #Larnacida# immediately follows the Larcarida as the next simple group of all #Larcoidea#; some genera of both groups (such as _Larnacalpis_ and _Coccolarcus_, or _Larnacantha_ and _Larcidium_) may easily be confounded from their being so much alike. In both the lentelliptical shell is composed of two concentric shells, an inner (medullary) and an outer (cortical) shell. But the connection between these shells and the construction of the inner shell is quite different in the two groups. Whilst in the Larcarida the medullary shell is connected with the cortical shell simply by radial beams, here in the Larnacida this connection is effected by two latticed lamellæ, which are the lateral wings of a transverse girdle. Therefore we encounter here for the first time that peculiar mode of growth which characterises the greater part of the #Larcoidea#, but particularly the Pylonida. But whilst in the Pylonida between the three crossed lattice-girdles, remain four open gates, here in the Larnacida the gates become closed by lattice-work; the lentelliptical cortical shell becomes perfect.

The most simple genus of Larnacida, and no doubt the common ancestral form of this whole family, is _Larnacilla_ (Pl. 50, figs. 1, 1_a_, 1_b_). The most important shell of this typical genus is composed of a simple lentelliptical medullary shell and of three elliptical latticed girdles surrounding it, perpendicular one to another. These three "dimensive girdles" lie in the perimeter of the three dimensive planes, the minor (and first) in the equatorial plane, the second (and major) in the lateral plane, the third (and intermediate) in the sagittal plane. Therefore we have before us the same "trizonal shell" as in the important genus _Trizonium_ among the Pylonida. But whilst in _Trizonium_, as in all Pylonida, the four gates between the girdles remain open, here in _Larnacilla_ they become perfectly closed by lattice-work.

The formation of the typical "_Larnacilla_-shell" begins with a simple, spherical or lentelliptical lattice-shell, from both sides of which arise two latticed "lateral wings" opposite on the poles of the transverse axis. These two wings are comparable to the lateral chambers of _Tholartus_ (among the Tholonida), but differ by two large openings. Each wing is a short cylindrical tube with latticed wall, open at both ends; the axis of the tube (going through the centre of the open ends) is parallel to the principal axis of the whole shell (and of the central chamber). Therefore both wings form together a transverse ring, the middle of which encloses the central chamber. The distal parts of both wings grow towards the poles of the principal axis; if they became united here, the second (lateral) girdle would be complete. Between it and the first girdle four open gates remain ("_Tetrapyle_"); but these become overgrown by the third or sagittal girdle, and at last the gates between this and the two other girdles become closed by lattice-work. This perfect fenestration of the trizonal cortical shell, and the complete closing of the gates between the girdles by network, is the only difference between _Trizonium_ and _Larnacilla_.

In _Larnacilla_ and in the nearly allied _Larnacidium_ (only differing by radial spines {616}on the surface) the "trizonal shell" is an external or "cortical shell," enclosing the central capsule, the interior of which only contains the simple central chamber and the jointed proximal parts of both lateral wings. In the other genera of Larnacida (by proceeding growth) this trizonal _Larnacilla_-shell becomes enclosed by the growing central capsule and is now only a "medullary shell," whilst on the outside of the central capsule in the same manner is developed an outer cortical shell (_Larnacalpis_, _Larnacantha_); and perhaps the same process may be repeated. But sometimes also this cortical shell becomes doubled by a simple envelop of network (_Larnacoma_). In the Larnacospongida the cortical shell is composed of a spongy framework (corresponding to the Spongolarcida in the foregoing family).

The lattice-work of the Larnacida is commonly irregular (as in most other #Larcoidea#), and its pores have little signification for the different species. On the outer surface often arise radial spines, symmetrically disposed either in dimensive planes or in diagonal planes.

The central capsule is constantly a true lentellipsis or a "triaxial ellipsoid," characterised by three halving, elliptical dimensive planes, perpendicular one to another. It bears a different relation to the skeleton in the two subfamilies of Larnacida. In the first subfamily, the Larnacillida (_Larnacilla_, _Larnacidium_), the central capsule encloses only the simple spherical or lentelliptical central chamber ("simple medullary shell"), and is enveloped by the trizonal cortical shell. In the other subfamily, the Larnacalpida (_Larnacalpis_, _Larnacospongus_, &c.), this trizonal "_Larnacilla_-shell" becomes enclosed by the overgrowing central capsule, which now becomes enveloped by an external, latticed or spongy, lentelliptical "cortical shell."

_Synopsis of the Genera of Larnacida._

-------------------------------------------------------------------------
I. Subfamily Larnacillida.
Medullary shell simple, spherical or subspherical. Cortical shell
lentelliptical, trizonal; between them four gates.
-------------------------------------------------------------------------
Shell without radial spines, 272. _Larnacilla_.

Shell with radial spines, 273. _Larnacidium_.
-------------------------------------------------------------------------
II. Subfamily Larnacalpida.
Medullary shell _Larnacilla_-shaped, double; the inner spherical or
subspherical, the outer lentelliptical and trizonal.
-------------------------------------------------------------------------
{ { Without radial
{ Cortical { spines, 274. _Larnacalpis_.
{ shell {
Cortical shell simple { simple. { With radial
or double, but not { { spines, 275. _Larnacantha_.
spongy. {
{ Cortical shell double,
{ without radial spines, 276. _Larnacoma_.

{ Shell without radial
Cortical shell simple { spines, 277. _Larnacospongus_.
or double, wholly or {
partly spongy. { Shell with radial spines, 278. _Larnacostupa_.

{617}Subfamily 1. LARNACILLIDA, Haeckel.

_Definition._--#Larnacida# with a simple, spherical or lentelliptical, medullary shell, connected by the lateral wings of a latticed transverse girdle with the simple lentelliptical trizonal cortical shell; the central capsule encloses the former and is enveloped by the latter.

Genus 272. _Larnacilla_,[311] n. gen.

_Definition._--#Larnacida# with a simple lentelliptical cortical shell, connected by the lateral wings of a latticed transverse girdle with the simple, spherical or lentelliptical, medullary shell. Surface without radial spines.

The genus _Larnacilla_ represents the most simple form of Larnacida, and at the same time the most important common ancestral form, from which the greater number of #Larcoidea# may be derived, viz., all those genera which possess the characteristic "_Larnacilla_-shaped medullary shell." This typical form of medullary shell may be derived from the genus _Trizonium_ among the Pylonida by the closing of the four open gates of this genus. The free opening of these four gates becomes overgrown and closed by lattice-work, developed from the free edges of the three crossed girdles, and thus finally all three girdles are united in the form of a simple lentelliptical shell (Pl. 50, figs. 1, 1_a_, 1_b_). Seen from the sagittal poles (or from the poles of the shortest axis, fig. 1), the shell exhibits on both sides of the small spherical medullary shell the two lateral wings of the transverse girdle from the face; seen from the lateral poles (or from the poles of the transverse axis, fig. 1_a_), one of these wings appears in the optical section as an oblong ring, which seemingly encloses the concentric medullary shell, and on both sides is grown together with the sagittal girdle; seen from the principal poles (or from the poles of the longitudinal axis, fig. 1_b_), both wings exhibit their elliptical opening (at the right and left from the central medullary shell). The two concentric shells are only connected by the two lateral tube-like wings of the transverse girdle; the lateral and the sagittal girdles have no connection with the medullary shell. The latter is sometimes spherical, at other times lentelliptical.

1. _Larnacilla typus_, n. sp. (Pl. 50, fig. 1, 1_a_, 1_b_).

Cortical shell with smooth surface and with subregular network; pores twice as broad as the bars; about twelve pores on the half meridian, ten on the half equator. Proportion of the three dimensive axes = 2 : 3 : 4. Internal four gates (between transverse and lateral girdles) roundish-triangular, little broader than high. Medullary shell spherical, scarcely one-third as broad as the lentelliptical cortical shell.

{618}_Dimensions._--Length of the cortical shell (or principal axis) 0.13, breadth of it (or transverse axis) 0.1, height of it (or sagittal axis) 0.07; pores 0.006, bars 0.003; medullary shell (diameter) 0.03.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

2. _Larnacilla prometor_, n. sp.

Cortical shell with rough surface and regular network; pores three times as broad as the bars; about ten on the half meridian, eight on the half equator. Proportion of the three axes = 1 : 2 : 3. Internal four gates (between transverse and lateral girdles) kidney-shaped, twice as broad as high. Medullary shell lentelliptical, of the same form as the external cortical shell, but only one third as large.

_Dimensions._--Length of the cortical shell 0.15, breadth 0.1, height 0.05, pores 0.015, bars 0.005; medullary shell 0.02 to 0.05.

_Habitat._--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

3. _Larnacilla subglobosa_, n. sp.

Cortical shell nearly spherical, with thorny surface and irregular network; pores roundish, twice to four times as broad as the bars; twelve to sixteen in the half circumference. Proportion of the three axes very little different = 1.3 : 1.4 : 1.5. Internal four gates elliptical, one and a half times as broad as high. Medullary shell spherical, one-fourth as broad as the cortical shell.

_Dimensions._--Length of the cortical shell 0.15, breadth 0.14, height 0.13; pores 0.006 to 0.012, bars 0.003; medullary shell 0.035.

_Habitat._--Pacific, central area. Station 266, depth 2750 fathoms.

4. _Larnacilla medullaris_, n. sp.

Cortical shell lentelliptical, with smooth surface and irregular network; pores roundish, very small, scarcely as broad as the bars; about eight to nine on the half meridian, six to seven on the half equator. Proportion of the three axes = 3 : 4 : 6. Internal four gates elliptical. Medullary shell spherical, scarcely one-third as broad as the cortical shell. (This small species may be only the medullary shell of some other Larcoid, the cortical shell of which is not yet formed.)

_Dimensions._--Length of the cortical shell 0.06, breadth 0.04, height 0.03; pores and bars about 0.004; medullary shell 0.013.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

Genus 273. _Larnacidium_,[312] n. gen.

_Definition._--#Larnacida# with a simple lentelliptical cortical shell, connected by the lateral wings of a latticed transverse girdle with the simple, spherical or lentelliptical, medullary shell. Surface armed with radial spines.

{619}The genus _Larnacidium_ has the same shell-formation as the foregoing _Larnacilla_, and differs from it only in the possession of radial spines on the surface, which in all known species exhibit a symmetrical disposition. From the nearly allied genus _Larcidium_ it differs in the characteristic mode of connection between the two shells, owing to the different kind of growth. In _Larcidium_ this connection is effected only by radial beams, whereas in _Larnacidium_ (as in all Larnacida) by two lateral latticed tubes, the wings of the primary transverse girdle.

1. _Larnacidium staurobelonium_, n. sp.

Cortical shell smooth, with four strong conical, radial spines in the lateral plane, opposite in pairs, two on the poles of the principal and two on the poles of the transverse axis. Pores subregular, circular, twice as broad as the bars; about twelve on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell spherical, one-third as broad as the cortical shell.

_Dimensions._--Length of the cortical shell 0.12, breadth 0.09, height 0.06; pores 0.008, bars 0.04; medullary shell 0.03.

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

2. _Larnacidium hexabelonium_, n. sp.

Cortical shell thorny, with six strong, three-sided pyramidal, radial spines, lying opposite in pairs on the poles of the three dimensive axes. Pores subregular, circular, three times as broad as the bars; about fourteen on the half meridian. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell spherical, one-third as broad as the cortical shell.