6. Toxarium furcatum, n. sp.
Galear bows simple, thoracal bows forked, both somewhat broader than the frontal bows. Shell therefore slightly constricted in the equatorial plane. Sagittal constriction rather deep, equal in the apical and basal parts. All bows armed with scattered spines, which are partly simple, partly forked.
Dimensions.—Length of the shell 0.14, breadth 0.16.
Habitat.—Central Pacific, Station 270, depth 2925 fathoms.
7. Toxarium pedatum, n. sp.
Galear bows simple, smaller than the frontal bows, which are again smaller than the thoracal bows. Therefore the breadth of the shell increases towards the base. Sagittal constriction flat in the apical part, deep in the basal part. All bows armed with small irregularly scattered spines; at the base six larger divergent feet (two lateral, two anterior, and two posterior).
Dimensions.—Length of the shell 0.17, breadth 0.15.
Habitat.—South Pacific, Station 295, depth 1500 fathoms.
Definition.—Galear and thoracal bows forked.
8. Toxarium costatum, n. sp.
Galear and thoracal bows forked, smaller than the frontal bows, all bows thorny, without larger spines. Sagittal constriction on both poles deep. Lateral outlines of the shell nearly parallel.
Dimensions.—Length of the shell 0.15, breadth 0.12.
Habitat.—Indian Ocean, Socotra (Haeckel), surface.
9. Toxarium bifurcum, n. sp. (Pl. 93, fig. 20).
Galear and thoracal bows forked, the former smaller than the frontal bows, the latter larger. Sagittal constriction rather flat on the apical pole, which bears a vertical forked horn, very deep on the basal pole of the primary ring. All bows armed with numerous spines, which are partly simple, partly forked, and mainly developed at the basal part of the thoracal bows.
Dimensions.—Length of the shell 0.2, breadth 0.2.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
Definition.—Tympanida with two bisected horizontal rings, connected by four vertical columellæ, which are bisected again by an equatorial ring.
The genus Microcubus is derived from its ancestral form Acrocubus by development of a third horizontal ring, which lies in the equatorial plane, parallel to the upper mitral and the lower basal ring. Whilst these latter are both bisected by the complete vertical sagittal ring, the equatorial ring is complete, and connected at the poles of the sagittal axis with the principal ring, and at the poles of the transverse axis with the frontal ring. Therefore the shell exhibits not eight large gates as in Acrocubus, but twelve, viz., four horizontal gates (two superior mitral and two inferior basal), four upper vertical gates (between the mitral and the equatorial ring), and four lower vertical gates (between the basal and the equatorial ring).
1. Microcubus dodecastoma, n. sp. (Pl. 94, fig. 9).
All twelve gates simple, irregularly ovate or pentagonal. Frontal ring on the sides concave, constricted by the equatorial ring. All rings curved, armed with short irregular thorns. No larger basal spines.
Dimensions.—Length of the shell 0.13, breadth 0.15.
Habitat.—Central Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms.
2. Microcubus pentacircus, n. sp.
All twelve gates simple. Frontal ring on the sides convex, not constricted by the equatorial ring. All rings tuberculate, with irregular roundish knots. No larger basal spines. Similar to the preceding species; but the five rings are much thicker and tuberculate (not thorny); the twelve gates are therefore relatively smaller.
Dimensions.—Length of the shell 0.1, breadth 0.12.
Habitat.—Fossil in Barbados.
3. Microcubus zonarius, n. sp. (Pl. 94, fig. 8).
All twelve gates simple, ovate. Frontal ring on the sides convex, not constricted by the equatorial ring, nearly twice as broad as long. All rings thorny, very thin, except only the broad angular sagittal ring. No larger basal spines.
Dimensions.—Length of the shell 0.08, breadth 0.15.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
4. Microcubus quadrupes, n. sp.
All twelve gates simple, square. Frontal ring square, not constricted by the equatorial ring. All rings smooth, quadrangular. Basal ring with four short vertical conical feet, two of which (right and left) are inferior prolongations of the frontal ring, and arise from the lateral corners of the basal gates; two others are prolongations of the sagittal ring (sternal and caudal), and arise from the medial corners of the basal gates. (The shell is like a small cube with four feet.)
Dimensions.—Length of the shell 0.13, breadth 0.11.
Habitat.—North Pacific, Station 253, depth 3125 fathoms.
5. Microcubus cornutus, n. sp.
Eight gates (two mitral, two basal, and four superior) simple; four inferior gates fenestrated by arachnoidal irregular threads. Frontal ring square, constricted on the sides by the equatorial ring. Basal ring with four short conical vertical feet, as in the preceding species. Sagittal ring with a vertical horn on the apex. All rings with small scattered thorns.
Dimensions.—Length of the shell 0.11, breadth 0.13.
Habitat.—North Pacific, Station 235, surface.
6. Microcubus amphispyris, n. sp. (Pl. 94, fig. 10).
Four gates (two mitral and two basal) simple; eight lateral gates (four superior and four inferior) fenestrated by arachnoidal irregular threads. Frontal ring convex, not constricted by the equatorial ring. Basal ring with six short conical divergent feet (two sagittal and four lateral). Sagittal ring with an apical horn. (Resembles some Spyroidea.)
Dimensions.—Length of the shell 0.08, breadth 0.12.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
Definition.—Tympanida with two bisected horizontal rings converging laterally and connected in the lateral poles of the equatorial plane. Eight large gates.
The genus Octotympanum differs from all other Tympanida in the peculiar connection of the two horizontal rings, which here reach the maximum of their growth, converge towards the equator, and come into direct contact on the poles of the equatorial transverse axis. Therefore the shell appears to be composed of three complete vertical meridian rings, the middle of which (the sagittal ring) is free and simple; the two other (subfrontal) rings are grown together at the lateral poles of the equatorial plane; commonly at these poles there arises (on the right and left) a strong lateral spine, and the base of this (or the crossing point of the two touching horizontal rings) corresponds to the remnants of the shortened frontal ring. The crown-shaped shell exhibits therefore eight large gates; two superior (mitral) and two inferior basal gates, two larger anterior (facial) and two larger posterior (occipital) gates. Seen from the lateral poles only two of the former are visible, and represent the figure of a vertical 8; seen from the sagittal poles, only two of the latter are visible, in the form of a larger horizontal eight. Octotympanum may be derived from Acrocubus by reduction of the lateral frontal ring to a knot (or cross-point), and by maximal extension of the two parallel horizontal rings, which become curved downwards laterally and touch at the lateral poles.
1. Octotympanum octospinum, n. sp.
Mitral gates smaller than the basal gates; upper halves of the two lateral meridional rings smaller than the lower halves. Rings with few scattered thorns; four larger simple spines, nearly horizontal in the equatorial plane; two on the poles of the sagittal axis, two on the poles of the lateral axis. Four other large spines, nearly vertical at the four lowermost basal points of the subfrontal rings.
Dimensions.—Length of the shell 0.09, breadth 0.12.
Habitat.—Central Pacific, Station 273, depth 2350 fathoms.
2. Octotympanum octonarium, n. sp. (Pl. 94, fig. 3).
Mitral gates of the same size as the basal gates; upper and lower halves of the meridional rings of equal size. Rings armed with numerous stout, thorny, simple and forked spines; four very large branched spines in the equatorial plane, nearly horizontal, two on the poles of the sagittal, two on the poles of the transverse axis, the latter curved downwards.
Dimensions.—Length of the shell 0.1, breadth 0.2.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
3. Octotympanum arborescens, n. sp.
Mitral gates smaller than the basal gates, the lower halves of the lateral rings being broader than the upper halves. Rings very spiny, armed with numerous branched spines; ten very large arborescent spines on the lateral rings; two on the poles of the transverse axis, eight on the prominent corners of the diagonal axes (four upper and four lower); sagittal ring thorny.
Dimensions.—Length of the shell 0.8, breadth 0.16.
Habitat.—Central Pacific, Station 274, depth 2750 fathoms.
4. Octotympanum cervicorne, n. sp. (Pl. 94, fig. 2).
Mitral and basal gates of equal size, the lower and upper halves of the two crossed lateral rings being nearly equal. Rings armed with numerous branched spines; two very large spines, similar to the antlers of a deer, on the poles of the lateral axis; their branches about half as large as the whole shell. Sagittal ring nearly smooth, with few small thorns on the poles of the main axis.
Dimensions.—Length of the shell 0.16, breadth 0.2.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
Definition.—Tympanida with two bisected horizontal rings, which are connected by three vertical meridional rings (or six columellæ).
The genus Tympaniscus and the following Tympanidium differ from all preceding Tympanida in the multiplication of the vertical columellæ, which connect the two horizontal bisected rings. Tympaniscus exhibits six columellæ, which may be regarded as halves of three meridional rings. Only one, however, of these is complete (the sagittal ring, which bisects the mitral and the basal ring); the two other meridional rings (placed in diagonal planes) may be regarded as produced by lateral bifurcation of an incomplete frontal ring; this appears to be already foreshadowed in the preceding Octotympanum.
1. Tympaniscus corona, n. sp.
Basal ring larger than the mitral ring, with numerous irregular short spines but without descending feet. Six columellæ strongly curved, in the lower half thicker and thorny; the four lateral much thinner than the two sagittal. Apex of the jointed sagittal ring with a conical horn.
Dimensions.—Length of the shell 0.08, breadth 0.11.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
2. Tympaniscus bipes, n. sp.
Basal ring of about the same size as the mitral ring, with two lateral descending feet, which are parallel and vertical, simple, without spur, half as long as the sagittal ring. The latter is ovate, twice as long and broad as the two circular frontal rings.
Dimensions.—Breadth of the shell 0.14, length 0.09.
Habitat.—North Pacific, Station 244, depth 2900 fathoms.
3. Tympaniscus dipodiscus, n. sp. (Pl. 94, figs. 5, 6).
Basal ring smaller than the mitral ring, with two lateral descending feet, which are nearly parallel and vertical, obtuse, about as long as the sagittal ring, and which bear on the outside a horizontal spur. Sagittal ring hexagonal, very stout, with a caudal appendix at the base, and with a small sagittal arch, bearing a stout spinulate double knob at the apex. The two subfrontal rings depressed, twice as broad as high, on the outside thorny, connected at each side in the lower half by a double transverse arch.
Dimensions.—Breadth of the shell 0.18, length 0.08 (with spines 0.18).
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.
4. Tympaniscus tripodiscus, n. sp. (Pl. 94, fig. 7).
Basal ring of about the same size as the mitral ring, with three large and stout divergent feet (two lateral and one caudal). Sagittal ring stout, broader than the two spiny subsagittal rings; the upper part of the latter bears two ascending arches, which are united with the large apical horn arising from the apex of the sagittal ring. Six columellæ nearly vertical, slightly curved on the outside; their lateral edges armed with numerous simple or forked spines.
Dimensions.—Breadth of the shell 0.1, total length 0.12.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
5. Tympaniscus quadrupes, n. sp. (Pl. 94, fig. 4).
Basal ring larger than the mitral ring, with four short vertical three-sided pyramidal feet of equal size (two lateral and two sagittal); the feet are three-sided pyramidal, with finely denticulate median edges, and bear at the base a horizontal thorny spur. Sagittal ring at the apex with a very large cross-shaped horn, bearing two horizontal thorny lateral branches; the horn is supported by an anterior and a posterior arch. Six columellæ strongly curved and dentate.
Dimensions.—Breadth of the shell 0.15, length 0.12.
Habitat.—South Pacific, Station 298, depth 2225 fathoms.
6. Tympaniscus fibula, Haeckel.
Ceratospyris fibula, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 3.
Basal ring of about the same size as the mitral ring, with six large conical descending feet; these are prolongations of the six columellæ, nearly of the same length, slightly divergent, and bear at the base a strong horizontal spur. The six columellæ are strongly curved, spiny, and bear above small arches, which are united with the apical horn of the sagittal ring.
Dimensions.—Breadth of the shell 0.09, height 0.05; total height 0.09.
Habitat.—Fossil in Barbados.
7. Tympaniscus dodecaster, n. sp.
Basal ring of the same size as the mitral ring, with six very large and six alternating smaller, slightly divergent, curved feet, about as long an the shell; the larger are the basal prolongations of the six curved, thorny columellæ. Mitral ring spiny, not overgrown with arches, as in the similar preceding species.
Dimensions.—Length of the shell 0.08, breadth 0.12.
Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.
Definition.—Tympanida with two bisected horizontal rings, which are connected by four vertical meridional rings (or eight columellæ).
The genus Tympanidium differs from all other Protympanida in the development of four vertical rings, placed in four different meridional planes. Only one of these is complete, the primary sagittal ring; the three others are incomplete, inserted on the two horizontal rings, which are formed by the paired mitral and basal branches of the sagittal ring; one of these three lies in the frontal plane, the two others in diagonal meridional planes (between the frontal and sagittal). The shell therefore exhibits twelve large gates, four of which are horizontal (the two superior mitral and the two inferior basal gates); the eight others are vertical, separated by the eight columellæ, or the halves of the four meridional rings. In the subgenus Tympanomma the number of gates amounts to sixteen, the four lateral gates being bisected by an incomplete equatorial ring. The genus Tympanidium may be derived from Acrocubus by development of the two diagonal rings (between the frontal and sagittal).
Definition.—Shell with twelve gates; the four lateral gates simple.
1. Tympanidium foliosum, n. sp. (Pl. 94, fig. 1).
Shell with twelve gates; the four lateral gates simple. Basal gates of the shell larger than the mitral gates. Sagittal ring ovate, much smaller than the three other meridional rings, which are armed with numerous large elegant spines, bearing a lanceolate leaf on a thin pedicle. The sagittal ring bears a bunch of similar spines only at the apex, and on both poles of the sagittal axis (in the equator) a single forked spine, with two thorny branches.
Dimensions.—Length of the shell 0.09 (with spines 0.25), breadth 0.15.
Habitat.—South Pacific, Station 300, depth 1375 fathoms.
2. Tympanidium spinosum, n. sp.
Shell with twelve gates; the four lateral gates simple. Basal and mitral gates of about equal size. Shell similar to that of the preceding species, differing mainly in the different armature; the numerous spines, covering the convex outside of the four vertical rings, are not leaf-shaped, but conical, short, of very variable size, partly simple, partly irregularly branched.
Dimensions.—Length of the shell 0.08 (with spines 0.2), breadth 0.12.
Habitat.—South Pacific, Station 295, depth 1500 fathoms.
Definition.—Shell with sixteen gates (eight median gates, paired on both sides of the sagittal ring, and eight lateral gates, paired on both sides of the frontal ring). The four lateral gates of the two preceding species (subgenus Tympanura) are bisected in Tympanomma by the lateral parts of an incomplete equatorial ring.
3. Tympanidium binoctonum, n. sp. (Pl. 94, fig. 18).
Shell with sixteen gates; the four lateral gates double, bisected by the lateral parts of an incomplete equatorial ring. Basal gates nearly rectangular, of the same breadth as the pentagonal mitral gates, but twice as long. Equatorial outline of the shell (seen in fig. 18 from the apical pole) octagonal. All rods of the shell thin, smooth.
Dimensions.—Transverse axis of the shell 0.1, sagittal axis 0.06.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.
4. Tympanidium barbadense, Haeckel.
"Hollow cylinder," &c., Bury, 1862, Polycystins of Barbados, pl. xvi. fig. 1.
Shell with sixteen gates; the four lateral gates double, bisected by an incomplete equatorial ring. Basal gates kidney-shaped, of the same breadth as the circular mitral gates, but twice as long. Equatorial outline of the shell elliptical. All rods of the shell thin, smooth.
Dimensions.—Transverse axis of the shell 0.12, sagittal axis 0.08.
Habitat.—Fossil in South Naparima, Trinidad, Barbados.
5. Tympanidium staurocircum, n. sp.
Shell with sixteen gates; the four lateral gates double, bisected by an incomplete equatorial ring. Basal and mitral gates of the shell of about equal size, roundish. Equatorial outline of the shell violin-shaped, with a sagittal constriction. All rods of the shell armed with short irregular spines.
Dimensions.—Transverse axis of the shell 0.12, sagittal axis 0.06.
Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.
Definition.—Tympanida with two fenestrated horizontal rings, which are connected by a variable number of vertical rods or columellæ. The shell therefore becomes more completely latticed than in the other Tympanida, and approaches that of the Spyroidea.
Definition.—Tympanida with two latticed horizontal rings, connected by numerous descending and diverging columellæ; mitral ring smaller than the basal ring.
The genus Paratympanum and the following nearly allied Lithotympanum form together the small subfamily of Paratympanida, distinguished from the other Tympanida by the fenestration of the two parallel horizontal rings. These rings in Lithotympanum are both equal, whilst in Paratympanum, the basal ring is larger than the mitral ring; therefore the connecting rods or columellæ are in the former parallel and vertical, in the latter divergent and descending. Two opposite ones of these columellæ are parts of the primary sagittal ring, two others are parts of the lateral or frontal ring, whilst the remainder are afterwards intercalated. Paratympanum may be derived from Dystympanium by fenestration of the basal ring.
1. Paratympanum hexastylum, n. sp.
Six divergent columellæ, about as long as the diameter of the hexagonal mitral ring, connect it with the larger hexagonal basal ring. Lattice of the mitral ring hemispherical, with six roundish pores, surrounding a central apical horn. Lattice of the basal ring with one large central pore, surrounded by numerous peripheral pores. Rings and rods smooth, without spines.
Dimensions.—Length of the shell 0.07; breadth of the mitral ring 0.06, of the basal ring 0.09.
Habitat.—Central Pacific, Station 266, depth 2750 fathoms.
2. Paratympanum octostylum, n. sp. (Pl. 94, fig. 14).
Eight divergent columellæ, about as long as the diameter of the octagonal mitral ring, connect it with the larger circular basal ring, and bear at each end a divergent, strong, conical spine. Lattice-plate of both rings slightly convex, with numerous subregular circular pores, smooth, without surface spines.
Dimensions.—Breadth of the mitral ring 0.06, of the basal ring 0.09.
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.
3. Paratympanum decastylum, n. sp.
Ten divergent columellæ, only half as long as the diameter of the decagonal mitral ring, connect it with the larger circular basal ring. Lattice-plate of the mitral ring nearly hemispherical of the basal ring flat, both with numerous irregular roundish pores and scattered spines. Margin of both rings spiny.
Dimensions.—Breadth of the mitral ring 0.08, of the basal ring 0.1.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
Definition.—Tympanida with two latticed horizontal rings, connected by numerous parallel and vertical columellæ; mitral and basal rings of equal size.
The genus Lithotympanum has the form of a cylindrical drum, the two fundamental faces of which (the mitral and basal gates) are closed by lattice-work. Both horizontal rings are equal, whilst in the preceding Paratympanum the basal gate is larger than the mitral. It may be derived from the latter by equalisation of these two rings, or directly from Dystympanium by fenestration of the basal ring.
1. Lithotympanum tuberosum, n. sp. (Pl. 83, fig. 1).
Both lattice-plates slightly convex; the mitral plate with six larger marginal pores and one central pore separated by numerous smaller pores; the basal plate with seven large pores only (one central and six peripheral). Surface and margin of the plates uneven, with roundish prominent dimpled tubercles. Both rings connected by ten to twelve simple cylindrical vertical columellæ.
Dimensions.—Length of the shell 0.13, breadth 0.1.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.
2. Lithotympanum spinosum, n. sp.
Both lattice-plates flat, with numerous irregular roundish pores of variable size. Surface thorny. Margin with numerous irregular spines, directed upwards on the mitral, downwards on the basal plate. Both rings connected by eight simple cylindrical vertical columellæ.
Dimensions.—Length of the shell 0.12, breadth 0.08.
Habitat.—Western Tropical Pacific, Station 224, depth 1850 fathoms.
Definition.—Tympanida with fenestrated mitral ring and simple open basal ring; both horizontal rings connected by numerous vertical or divergent columellæ.
Definition.—Tympanida with two horizontal rings, connected by numerous (six to eight or more) divergent columellæ. The upper mitral ring is smaller and latticed, the lower basal ring larger and open.
The genus Dystympanium, representing a peculiar subfamily, differs from all other Tympanida in the different shape of the two parallel horizontal rings. The upper or mitral ring is closed by a lattice-plate (as in Paratympanum), the lower or basal ring is simple and open (as in Eutympanium). Dystympanium may therefore be regarded as an intermediate form between these two genera, and may perhaps be derived from Paratympanum by loss of the lower lattice-plate.
1. Dystympanium dictyocha, n. sp. (Pl. 94, figs. 15, 16).
Basal ring circular, with eighteen to twenty short conical divergent spines. Mitral ring about two-thirds as broad, hexagonal, with six ascending spines on the six corners. The latter are connected with the former by six simple, straight, obliquely descending columellæ, about as long as the diameter of the mitral ring. Mitral lattice-plate slightly convex, with seven roundish pores (six peripheral pores around a central pore).
Dimensions.—Diameter of the basal ring 0.09, mitral ring 0.06; length of the columellæ 0.05.
Habitat.—Tropical Atlantic, Station 338, depth 1990 fathoms.
2. Dystympanium distephanus, n. sp.
Basal ring hexagonal, with six larger spines at the six corners, and numerous smaller ones between them. Mitral ring half as broad as the basal ring, also with six angular spines. The latter are connected with the former by six divergent curved columellæ, about as long as the diameter of the basal ring. Mitral lattice-plate flat, with irregular roundish pores.
Dimensions.—Diameter of the basal ring 0.1, mitral ring 0.05; length of the columellæ 0.09.
Habitat.—Equatorial Atlantic, Station 347, depth 2250 fathoms.
3. Dystympanium medusa, n. sp.
Basal ring circular, with eight larger and numerous smaller divergent spines. Mitral ring two-thirds as broad as the basal ring, octagonal, with eight conical ascending spines on the eight corners. The latter are connected with the former by eight divergent, curved columellæ, as long as the diameter of the mitral ring. Mitral lattice-plate nearly hemispherical, with nine circular pores (eight peripheral pores around one central pore).
Dimensions.—Diameter of the basal ring 0.12, mitral ring 0.08; length of the columellæ 0.09.
Habitat.—South Atlantic, Station 332, depth 2200 fathoms.
Definition.—Tympanida with two simple horizontal rings, which are connected by a variable number of vertical rods or columellæ. Therefore the shell exhibits a large simple mitral gate on the upper, and a large simple basal gate on the lower side; between the two a variable number of lateral gates.
Definition.—Tympanida with two simple horizontal rings, connected by two vertical columellæ.
The genus Parastephanus is the simplest among the Eutympanida, and exhibits only two vertical rods or columellæ, which connect the two parallel horizontal rings. One of these latter must be regarded as the mitral or superior ring, the other as the basal or inferior ring; whilst the two parallel columellæ, connecting both, are the remaining vertical parts of the sagittal ring, the upper and lower parts of which are lost. By loss of the latter Parastephanus has probably been derived from Protympanium.
1. Parastephanus circularis, n. sp.
Two horizontal rings smooth, circular, of equal size, connected by two curved smooth columellæ, which are somewhat shorter than the diameter of the rings.
Dimensions.—Diameter of the rings 0.08, length of the columellæ 0.06.
Habitat.—Central Pacific, Station 263, depth 2650 fathoms.
2. Parastephanus quadrispinus, n. sp. (Pl. 93, fig. 21).
Two horizontal rings smooth, elliptical or nearly circular, of equal size, connected by two vertical, slightly curved columellæ, which are about as long as the radius of the rings. Each ring bears two simple lateral spines, which in the mitral ring are curved downwards, in the basal ring upwards, possibly the last remains of a reduced frontal ring.
Dimensions.—Diameter of the rings 0.09, length of the columellæ 0.05.
Habitat.—North Pacific, Station 236, surface.
3. Parastephanus asymmetricus, n. sp. (Pl. 82, fig. 10).
Two horizontal rings thorny, of equal size, irregularly ovate or nearly semicircular, and of somewhat asymmetrical form. The two connecting parallel columellæ are straight, cylindrical, about as long as the diameter of the rings. The peculiar asymmetry in the form of the rings raises the possibility that the two columellæ in this species are the remaining parts of a frontal ring, and that the sagittal ring has altogether disappeared. In this case the convex half of both rings would be the ventral, the straight half the dorsal part.
Dimensions.—Diameter of the rings 0.1, length of the columellæ 0.08.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
4. Parastephanus dispar, n. sp.
Two horizontal rings elliptical, thorny, of different sizes, the basal ring one and a half times as broad as the mitral ring. The two connecting columellæ are curved, somewhat longer than the diameter of the mitral ring.
Dimensions.—Diameter of the basal ring 0.09, mitral 0.06; length of the columellæ 0.07.
Habitat.—South Pacific, Station 300, depth 1375 fathoms.
Definition.—Tympanida with two simple horizontal rings, connected by three vertical columellæ.
The genus Prismatium was hitherto the only known form of the Tympanida, and the only species described in 1862 in my Monograph was Prismatium tripleurum (loc. cit., p. 270, pl. iv. fig. 6). A new species from the Challenger collection (Pl. 93, fig. 22), Prismatium tripodium, explains the true structure of this remarkable genus. The skeleton is composed of nine siliceous rods, corresponding to the edges of a trilateral prism. Six of these are horizontal, and enclose the two parallel triangular horizontal gates, the superior of which is formed by the mitral or coryphal, and the inferior by the basal or cortinar ring. The three other rods are vertical and nearly parallel, and connect (as lateral edges of the prism) the corresponding corners of the two parallel horizontal triangles. Two of these vertical columellæ, together with the two horizontal parallel rods connecting them, represent the complete frontal ring, whilst the third vertical columella is the posterior half of the sagittal ring, the other parts of which are lost.
1. Prismatium tripodium, n. sp. (Pl. 93, fig. 22).
Mitral ring triangular, somewhat smaller than the triangular basal ring, both connected at the corners by three vertical, slightly curved columellæ. From the six corners arise six radial spines of different size and form; the two paired spines of the mitral ring are simple and very small, whilst those of the basal ring are three times as long and bear a lateral branch. The odd spine of the third corner is on both rings larger, and distinguished by some thorns. This difference seems to indicate that these two odd spines correspond to the apical horn and the caudal foot of Cortina, and the columella between them is the rest of the reduced sagittal ring. In this case the quadrangular vertical ring, which is composed of the two paired columellæ and the two connecting horizontal rods, would be probably the frontal ring.
Dimensions.—Length of the shell 0.09, breadth 0.07.
Habitat.—Equatorial Atlantic, Station 347, surface.
2. Prismatium tripleurum, Haeckel.
Prismatium tripleurum, Haeckel, 1862, Monogr. d. Radiol., p. 270, Taf. iv. fig. 6.
Acanthodesmia prismatium, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 799.
Mitral and basal rings of equal size, equilateral triangular, both connected at the corners by three vertical equal columellæ. From the six corners arise six short, equal, conical radial spines. The nine rods of the shell correspond to the nine edges of a triangular equilateral prism.
Dimensions.—Length of the shell 0.044, breadth 0.032.
Habitat.—Mediterranean (Messina), surface.
Definition.—Tympanida with two simple horizontal rings of different sizes, connected by four divergent columellæ.
The genus Pseudocubus exhibits the characteristic form of an obelisk, or a truncated four-sided pyramid. The four edges of this obelisk, or the four "columellæ," are the remaining parts of the two incomplete vertical rings; two opposite edges are the dorsal and ventral rod of the sagittal ring; the two alternate edges between these are the lateral rods of the frontal ring. The two horizontal rings, which become connected by the four divergent columellæ, are the smaller mitral ring and the larger basal ring; both are either square or nearly circular.
1. Pseudocubus obeliscus, n. sp. (Pl. 94, fig. 11).
Mitral ring square, with circular gate and two divergent simple spines on each corner. Basal ring twice as broad, square, with four convex sides and one simple spine on each corner. Four columellæ straight. All twelve rods with three smooth edges.
Dimensions.—Breadth of the mitral ring 0.02, of the basal ring 0.05.
Habitat.—Central Pacific, Station 266, depth 2750 fathoms.
2. Pseudocubus octostylus, n. sp.
Mitral ring square, with one stout pyramidal spine on each corner. Basal ring twice as broad, square, also with a single strong spine on each corner. Four columellæ straight. All twelve rods with three smooth edges.
Dimensions.—Breadth of the mitral ring 0.04, of the basal ring 0.08.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
3. Pseudocubus hexapylus, n. sp. (Pl. 94, fig. 12).
Mitral ring circular, two-thirds as broad as the subcircular, or nearly square, basal ring; both rings with a simple spine on the two sagittal corners (dorsal and ventral), with a forked or branched larger spine on the two lateral corners (right and left). All twelve rods more or less curved and thorny.
Dimensions.—Breadth of the mitral ring 0.07, of the basal ring 0.1.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
Definition.—Tympanida with two simple horizontal rings of equal size, connected by four parallel vertical columellæ.
The genus Lithocubus is very remarkable for the regular cubical form of the skeleton, which is composed of twelve siliceous rods, corresponding to the twelve edges of a cube. Eight of these are horizontal, and enclose the two parallel square horizontal gates, the superior mitral and the inferior basal gate. The four other rods are vertical, parallel, and connect (as lateral edges of the cube) the corresponding corners of the two horizontal squares. Two opposite ones of these four vertical columellæ are the remaining halves of the incomplete sagittal ring; the two alternate are the remaining halves of the incomplete frontal ring. The four lateral gates between these four columellæ are also square or rectangular, and either of the same size as the two horizontal gates, or somewhat larger. Lithocubus may be derived from Acrocubus by reduction of the coryphal and the basal part of the primary sagittal ring, the only remaining parts of which are the anterior and the posterior columellæ.
1. Lithocubus geometricus, n. sp. (Pl. 94, fig. 13).
The twelve rods, corresponding to the edges of the geometrical cube, are straight and smooth; the eight corners provided with a small conical thorn. The shell exhibits six equal square sides, and represents therefore exactly the geometrical form of a cube.
Dimensions.—Diameter of the cube 0.05; thickness of the bars 0.008.
Habitat.—Tropical Pacific, Station 224, depth 1850 fathoms.
2. Lithocubus octacanthus, n. sp.
The twelve rods of the cubical shell are slightly curved, convex, smooth, as in the similar preceding species. It differs from that in the development of eight slender radial spines, arising from the eight corners of the geometrical cube, from two to three times as long as its diameter, and lying opposite in pairs in its diagonals.
Dimensions.—Diameter of the cube 0.06; length of the spines 0.15.
Habitat.—North Atlantic, Canary Islands, surface.