The genus Coronidium and the following, nearly allied Acanthodesmia, form together the peculiar subfamily of Acanthodesmida—not in the wider sense in which I first founded this group (1862, Monogr. d. Radiol., p. 265), but in the restricted sense, which is exactly defined in my Prodromus (1881, p. 445). According to this definition, the shell is composed of three different rings, perpendicular to one another; only one of these is complete, the simple horizontal basal ring; the two others are incomplete and vertical (the primary or sagittal and the secondary or frontal ring). Therefore there remain constantly between the three rings five characteristic large openings or gates; four of these are lateral (between the halves of the two meridional rings), the fifth is basal, enclosed by the horizontal basal ring. The longest known type of this subfamily is Acanthodesmia vinculata, the five characteristic gates of which are clearly distinguished by its discoverer, Johannes Müller ("Das Gehäuse besteht nur aus den Leisten zwischen fünf grossen Lücken"). The Acanthodesmida may be derived from the Eucoronida by reduction of the basilar rod of the sagittal ring. If in Eucoronis this basal rod be lost, Coronidium arises.
1. Coronidium dyostephanus, n. sp. (Pl. 82, fig. 7).
Frontal ring elliptical, with few scattered thorns, twice as broad as high, and three times as broad as the smooth rhombic basal ring. Sagittal ring semicircular, very stout, twice as thick as the two other rings, with short lateral thorns (in the figure seen from the apical pole, which exhibits a four-lobed dimple). Basal gate rhombic.
Dimensions.—Height of the frontal ring 0.08, breadth 0.16.
Habitat.—Central Pacific, Station 263, depth 2650 fathoms.
2. Coronidium diadema, n. sp. (Pl. 82, fig. 8).
Frontal ring kidney-shaped, one and a half times as broad as high, with a slight sagittal constriction. Sagittal ring ovate, smaller, about of the same size as the elliptical basal ring. Rods of all three rings cylindrical, bearing numerous short and stout curved spines, partly simple, partly branched. Four bunches of larger spines on the four corners of the basal ring, and one very large bunch on the apical pole. Basal gate elliptical, one and a half times as broad as long.
Dimensions.—Height of the frontal ring 0.13, breadth 0.18.
Habitat.—Indian Ocean (Madagascar), Rabbe, surface.
3. Coronidium cervicorne, n. sp. (Pl. 82, fig. 1).
Frontal ring kidney-shaped, twice as broad as high, one and a half times as broad as the elliptical basal ring, both with a slight sagittal constriction. Sagittal ring ovate. All three rings (in the figure seen from the apical pole) with cylindrical rods, armed with numerous stout spines, branched like a deer's antler. Basal gate rather oblong, twice as broad as long.
Dimensions.—Height of the frontal ring 0.08, breadth 0.16.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
4. Coronidium acacia, n. sp. (Pl. 82, fig. 2).
Frontal ring and sagittal ring nearly circular, of equal size, truncated at the base. Basal ring circular, somewhat smaller. All three rings with prominent edges, bearing bunches of short and straight pointed spines, like those of an Acacia. Basal gate circular.
Dimensions.—Height of the frontal ring 0.12, breadth 0.14.
Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.
Definition.—Coronida with five large, partly latticed gates (four lateral and one basal). Skeleton composed of two incomplete, partly fenestrated meridional rings, and one complete basal ring.
The genus Acanthodesmia, the oldest known form of all Coronida, differs from the preceding Coronidium, its ancestral form, in the development of irregular loose lattice-work along the rings, and therefore bears to it the same relation that Zygostephanium does to Zygostephanus. The first species described by Johannes Müller, Acanthodesmia vinculata ("with five large gates between the bars of the shell") remains the true type of this genus; the second species described by him (Acanthodesmia dumetum) belongs to the Plectanida (Polyplecta).
1. Acanthodesmia vinculata, J. Müller.
Acanthodesmia vinculata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 30, Taf. i. figs. 4-6 (non 7).
Lithocircus vinculatus, J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 484.
Frontal ring violin-shaped, one and a half times as broad as high, with a sagittal constriction. Sagittal ring ovate, smaller. The four gates between the two rings are partly fenestrated by a few thin threads, irregularly branched and connecting the two rings. A few short thorns are scattered here and there. Basal gate elliptical.
Dimensions.—Height of the frontal ring 0.12, breadth 0.18.
Habitat.—Mediterranean (Nice), Atlantic (Canary Islands), surface.
2. Acanthodesmia ceratospyris, n. sp.
Frontal ring violin-shaped, one and a half times as broad as high, with a deep sagittal constriction. Sagittal ring semicircular, half as high as the frontal ring. The four gates between the two rings are partly fenestrated by anastomosing branches of the numerous, irregularly branched spines, which cover all three rings. Basal gate nearly circular, smaller than the sagittal ring.
Dimensions.—Height of the frontal ring 0.08, breadth 0.12.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
3. Acanthodesmia corona, n. sp. (Pl. 93, fig. 5).
Frontal ring kidney-shaped, nearly twice as broad as high, with a flat sagittal constriction. Sagittal ring semicircular. The four gates between the two rings are partly fenestrated by an arachnoidal network, composed of thin, irregularly branched threads, arising from the rings. The edges of all three rings are armed with irregular thorns. Basal gate circular, larger than the sagittal ring.
Dimensions.—Height of the frontal ring 0.08, breadth 0.14.
Habitat.—Indian Ocean (Madagascar), Rabbe, surface.
4. Acanthodesmia mülleri, n. sp.
Frontal ring kidney-shaped with a deep sagittal constriction. Sagittal ring ovate. The four gates between the two rings irregularly fenestrated, with a few large polygonal meshes. Edges of the rings with a few scattered thorns. Basal gate violin-shaped.
Dimensions.—Height of the frontal ring 0.1, breadth 0.16.
Habitat.—Tropical Atlantic, Station 347, surface.
Definition.—Coronida with six large gates (four lateral and two basal gates). Skeleton composed of three rings perpendicular to one another, two of which are complete (the vertical sagittal, and the horizontal basal ring); the third is incomplete (the vertical frontal ring).
Definition.—Coronida with six large simple gates (four lateral and two basal). Skeleton composed of two complete rings (the sagittal and basal) and one incomplete (frontal) ring. Basal ring without typical feet.
The genus Eucoronis and the following two nearly allied genera (Plectocoronis and Podocoronis) compose together the important subfamily Eucoronida. In this typical main group of Coronida the shell is constantly composed of three rings and six gates. The vertical sagittal ring and the horizontal basal ring are complete (as in the Semantida); the vertical frontal ring is incomplete. Between these three rings remain six large open gates, the four upper (or lateral) are always much larger than the four lower (or basal gates). Eucoronis may be derived from Semantis by development of the frontal ring.
Definition.—Rings smooth or rough, armed with numerous short spines or thorns.
1. Eucoronis perspicillum, n. sp. (Pl. 82, fig. 6).
Frontal ring elliptical, twice as broad as high, with a slight constriction at the apical pole, armed with three pairs of short conical spines, one apical pair (near the constriction) and two lateral pairs (one upper and one lower pair). Sagittal ring of the same height, half the breadth and double the thickness, also armed with three pairs of spines (one basal, one dorsal, and one ventral pair).
Dimensions.—Height of the frontal ring 0.11, breadth 0.22.
Habitat.—Central Pacific, Stations 265 to 268, depth 2700 to 2900 fathoms.
2. Eucoronis lævigata, n. sp.
Frontal ring elliptical, smooth, one and a half times as broad as high, without sagittal constriction, with horizontal basal gates. Sagittal ring of the same height and thickness, also elliptical and smooth. No spines on either of the smooth rings.
Dimensions.—Height of the frontal ring 0.1, breadth 0.15.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.
3. Eucoronis nephrospyris, n. sp. (Pl. 82, fig. 5).
Frontal ring kidney-shaped, in the upper half convex, in the lower concave, with a sagittal constriction (often much deeper than in the specimen figured). Sagittal ring ovate, about two-thirds as high as the frontal ring. Rods of both rings without edges, cylindrical, armed with numerous short conical thorns.
Dimensions.—Height of the frontal ring 0.1 to 0.12, breadth 0.15 to 0.18.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, many Stations, surface and at various depths.
4. Eucoronis angulata, n. sp. (Pl. 82, fig. 3).
Frontal ring violin-shaped, twice as broad as high, on the upper and the lower margin concave, with a deep sagittal constriction. Sagittal ring pentagonal, with straight horizontal basal rod, two-thirds as high as the frontal ring. Rods of both rings with sharp prominent edges, bearing numerous short pyramidal spines.
Dimensions.—Height of the frontal ring 0.09, breadth 0.17.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
Definition.—Rings armed with numerous large, branched or arborescent spines.
5. Eucoronis cervicornis, n. sp.
Frontal ring kidney-shaped, in the upper half convex, in the lower concave, with sagittal constriction. Sagittal ring ovate, two-thirds as high as the frontal ring. Both rings armed with numerous stout spines, irregularly branched like a deer's antler. (Very similar to Coronidium cervicorne, Pl. 82, fig. 1, which I formerly confounded with it, but differing in the complete sagittal ring, which in the latter form is incomplete and has lost its basal part.)
Dimensions.—Height of the frontal ring 0.12, breadth 0.2.
Habitat.—Central Pacific, Station 264, surface.
6. Eucoronis arborescens, n. sp.
Frontal ring kidney-shaped, with a deep sagittal constriction in the concave basal part. Sagittal ring ovate, half as high as the frontal ring. Both rings armed with numerous thin, richly branched and arborescent spines (branches much thinner and more numerous than in the preceding and following species).
Dimensions.—Height of the frontal ring 0.15, breadth 0.25.
Habitat.—Equatorial Atlantic, Station 247, surface.
7. Eucoronis challengeri, n. sp. (Pl. 82, fig. 4).
Lithocoronis challengeri, Haeckel, 1881, Prodromus, p. 445.
Frontal ring violin-shaped, one and a half times as broad as high, with a strong sagittal constriction. Sagittal ring nearly circular, two-thirds as high as the frontal ring. Both rings armed with numerous irregularly branched spines. (The specimen figured, with red central capsule and numerous xanthellæ, was observed living by me at the Canary Islands.)
Dimensions.—Height of the frontal ring 0.1 to 0.12, breadth 0.14 to 0.17.
Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, surface and at various depths.
Definition.—Coronida with six large, partly latticed gates (four lateral and two basal). Skeleton composed of two complete rings (the sagittal and basal) and one incomplete (frontal) ring. Basal ring without developed typical feet.
The genus Plectocoronis differs from the preceding Eucoronis, its ancestral form, in the development of loose irregular lattice-work along the two meridional rings, and therefore bears to it the same relation that Acanthodesmia does to Coronidium. If the lattice-work become more complete and close the gates, these Coronida pass over directly into Spyroidea (Zygospyrida).
1. Plectocoronis anacantha, n. sp.
Basal ring and frontal ring elliptical, without sagittal constriction. Sagittal ring ovate. The frontal and sagittal rings are bordered on both edges with an incomplete series of small irregular pores. All three rings smooth, without spines.
Dimensions.—Height of the frontal ring 0.1, breadth 0.16.
Habitat.—Central Pacific, Station 274, depth 2750 fathoms.
2. Plectocoronis triacantha, n. sp.
Basal ring and frontal ring nearly circular, without sagittal constriction. Sagittal ring elliptical, prolonged at the apex into an apical horn from which two branched lateral bows descend and unite with the uppermost parts of the frontal ring. Four other small bows descend from the lowermost parts of the latter and unite with the basal ring. From the lateral corners of the basal ring descend two short vertical feet. (May be regarded as derived from Podocoronis toxarium, Pl. 83, Fig. 7, by development of the bows connecting the rings.)
Dimensions.—Height of the frontal ring 0.11, breadth 0.13.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
3. Plectocoronis pentacantha, n. sp. (Pl. 93, fig. 6).
Basal ring and frontal ring kidney-shaped, with deep sagittal constriction. Sagittal ring ovate, prolonged at the apex into an oblique horn. From the edges of the angular rings delicate threads arise, which anastomose and form irregular arachnoidal meshes, partly closing the four open lateral gates. Two basal gates simple. From the four nodal points of the basal ring there arise four, short diverging feet, comparable to rudimentary cortinar feet (two lateral from the frontal ring and two sagittal from the primary ring, as basal prolongations).
Dimensions.—Height of the frontal ring 0.12, breadth 0.18.
Habitat.—Central Pacific, Station 271, surface.
Definition.—Coronida with six large gates (four lateral and two basal). Skeleton composed of two complete rings (the sagittal and basal) and one incomplete (frontal) ring. Basal ring provided with typical, regularly disposed, descending feet (cortinar feet).
The genus Podocoronis differs from the two preceding nearly allied genera in the development of typical radial feet on the basal ring, which by their regular disposition and their general appearance among the Spyroidea and Cyrtoidea obtain great morphological importance. According to the different number and disposition of these basal feet (or "cortinar feet"), the following subgenera may be distinguished (regarded in my Prodromus, 1881, p. 445, as separate genera):—Dipocoronis with two lateral feet, Tripocoronis with three cortinar feet (most important!), Tetracoronis with four crossed feet, Hexacoronis with six radial feet, Stylocoronis with numerous (8 or more feet). These subgenera have important relations to the corresponding genera of Zygospyrida.
Definition.—Basal ring with two descending lateral feet (right and left) as prolongations of the frontal ring.
1. Podocoronis dipodiscus, n. sp.
Basal ring nearly circular, with two conical, straight, parallel descending feet, which are direct lateral prolongations of the subcircular frontal ring, and half as long as it. The ovate sagittal ring bears at the apex a short conical vertical horn. All rings nearly smooth.
Dimensions.—Height of the frontal ring 0.12, breadth 0.14.
Habitat.—Central Pacific, Station 266, depth 2750 fathoms.
2. Podocoronis toxarium, n. sp. (Pl. 83, fig. 7).
Basal ring elliptical, with two descending, slightly curved conical feet, lateral prolongations of the subcircular frontal ring. The ovate sagittal ring bears at the apex a cylindrical vertical horn, which is connected by two descending lateral arches (or galear arches) with the uppermost part of the frontal ring.
Dimensions.—Height of the frontal ring 0.1, breadth 0.13.
Habitat.—Central Pacific, Stations 265 to 268, depth 2900 fathoms.
Definition.—Basal ring with three descending feet (one caudal and two pectoral).
3. Podocoronis cortiniscus, n. sp. (Pl. 97, fig. 2).
Basal ring violin-shaped, with three straight divergent thorny feet, about as long as the ovate sagittal ring. The dorsal part of the latter is straight, vertical, and prolonged downwards into the caudal foot, upwards into a stout, thorny, vertical apical horn. The ventral part is semicircular and gives off the lateral branches, forming the kidney-shaped sagittal ring. All the rings and their apophyses are armed with stout thorns. This and the following tripodal species may be directly derived from Cortina.
Dimensions.—Height of the frontal ring 0.1, breadth 0.15.
Habitat.—Central Pacific, Station 274, depth 2750 fathoms.
4. Podocoronis tripodiscus, n. sp.
Basal ring kidney-shaped, with three large divergent curved feet, nearly twice as long as the semicircular sagittal ring. The straight dorsal part of the latter is prolonged downwards into the caudal foot, upwards into a large branched apical horn, curved backwards. Differs from the preceding species mainly in the longer curved apophyses and in the larger violin-shaped frontal ring.
Dimensions.—Height of the frontal ring 0.12, breadth 0.2.
Habitat.—North Pacific, Station 238, surface. Fossil in Barbados.
Definition.—Basal ring with four descending feet (two sagittal and two lateral).
5. Podocoronis tetrapodiscus, n. sp.
Basal ring kidney-shaped, with four stout and straight divergent feet, about as long as the sagittal ring; two of them are lateral and arise from the basal corners of the violin-shaped frontal ring (at its junction with the basal ring); two are sagittal, and arise from the basal corners of the semicircular sagittal ring (one posterior caudal and one anterior sternal). The straight dorsal part of the sagittal ring is prolonged upwards into an apical horn. All the rings are thorny.
Dimensions.—Height of the frontal ring 0.15, breadth 0.25.
Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.
Definition.—Basal ring with six radial descending feet (two sagittal, two pectoral, and two tergal feet).
6. Podocoronis hexapodiscus, n. sp.
Basal ring violin-shaped, with six conical, vertically descending feet, half as long as the sagittal ring; two of them are sagittal (arising from the two basal corners of the sagittal ring, caudal and sternal feet); the other four are lateral, and prolongations of the forked basal parts of the frontal ring, which is inserted on the basal ring with two forked branches; the anterior correspond to the pectoral, the posterior to the tergal feet of Hexaspyris. All the rings are thorny.
Dimensions.—Height of the frontal ring 0.11, breadth 0.17.
Habitat.—South Pacific, Station 295, depth 1500 fathoms.
Definition.—Basal ring with numerous (eight to twelve or more) descending feet.
7. Podocoronis petalospyris, n. sp.
Basal ring violin-shaped, with ten to twelve flat lamellar, vertically descending feet, about as long as the ovate sagittal ring. Frontal ring twice as broad as long, elliptical. All rings nearly smooth. Similar to a Petalospyris without lattice-work.
Dimensions.—Height of the frontal ring 0.1, breadth 0.2.
Habitat.—Fossil in Barbados.
8. Podocoronis polypodiscus, n. sp.
Basal ring elliptical, with fifteen to eighteen conical, curved, descending feet, half as long as the ovate sagittal ring. Frontal ring kidney-shaped, one and a half times as broad as long. All the rings armed with short conical spines.
Dimensions.—Height of the frontal ring 0.12, breadth 0.18.
Habitat.—Central Pacific, Station 273, depth 2350 fathoms.
Definition.—Coronida with eight large gates (four superior lateral and four inferior basal). Skeleton composed of three complete rings, perpendicular to one another; two of which are vertical (the primary or sagittal and the secondary or frontal ring), the third is horizontal (the tertiary or basal ring).
Definition.—Coronida with eight large, simple gates of different sizes; the four upper or lateral gates larger than the four lower or basal gates. Skeleton composed of three simple complete rings, perpendicular to one another.
The genus Tristephanium, and the three following genera derived from it, represent together the interesting subfamily of Trissocyclida (Prodromus, 1881, p. 446). These differ from all other Coronida in the possession of three complete rings, perpendicular to one another. The first of these is the vertical sagittal ring, the second the vertical frontal ring, and the third the horizontal basal ring. Since these three rings lie in the three dimensive planes, they are perpendicular to one another; and between them remain eight large open gates. Originally the four upper or lateral gates (corresponding to those of Zygostephanus) are much larger, the four lower or basal gates (corresponding to those of Semantrum) much smaller; but afterwards the latter may reach the size of the former, so that the basal ring becomes equatorial (in Trissocircus and Trissocyclus). The common ancestral form of the Trissocyclida (Tristephanium) may be derived directly either from Semantrum (by complete development of the frontal ring) or from Eucoronis (by complete development of four basal gates).
Definition.—Sagittal and frontal ring of different size and form.
1. Tristephanium dimensivum, n. sp. (Pl. 93, fig. 9).
Sagittal ring ovate, with a large thorny apical horn, smaller than the two other rings. Frontal ring violin-shaped, with a deep sagittal constriction. Basal ring also violin-shaped, in the sagittal axis constricted. Its four gates (two jugular and two cardinal) of nearly equal size. All three rings angular, armed with scattered, stout, thorny spines, which are larger in the basal half.
Dimensions.—Height of the frontal ring 0.08, breadth 0.12.
Habitat.—North Pacific, Station 241, depth 2300 fathoms.
2. Tristephanium octopyle, n. sp. (Pl. 93, fig. 8).
Sagittal ring ovate, nearly smooth, smaller than the two other rings. Frontal ring kidney-shaped, with a deep basal constriction. Basal ring violin-shaped. The jugular gates about half as large as the cardinal gates. Rods of the rings cylindrical, with few scattered thorns.
Dimensions.—Height of the frontal ring 0.09, breadth 0.14.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
3. Tristephanium hertwigii, Haeckel.
Acanthodesmia hertwigii, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. pp. 499, 539, Taf. xxxii. figs. 9a-9c.
Sagittal ring ovate or nearly semicircular; its dorsal rod straight, smooth (fig. 9c, a), its ventral rod (b) curved, thorny. Frontal ring much larger, thorny, violin-shaped, with a slight sagittal constriction. Basal ring smaller than the sagittal ring, thorny, kidney-shaped, with four different gates; the two cardinal pores much larger than the two jugular pores. (The four basal pores are often much larger than in the specimen figured by Bütschli. Also the number, form, and size of the spines is very variable.)
Dimensions.—Height of the frontal ring 0.07 to 0.09, breadth 0.17 to 0.2.
Habitat.—Fossil in Barbados.
Definition.—Sagittal and frontal ring of equal size and form.
4. Tristephanium quadricorne, n. sp. (Pl. 93, fig. 7).
Sagittal and frontal ring of equal size and form, larger than the circular basal ring. From the four corners, in which the latter crosses the two former, arise four strong, divergent spines, branched like a deer's antler. Some smaller spines are scattered on the rings, and a bunch of four spines arises on the apical pole. The four upper gates are triangular, the four lower nearly semicircular, the latter of equal size, half as large as the former.
Dimensions.—Height of the frontal ring 0.13, breadth 0.14.
Habitat.—South Atlantic, Station 342, depth 1445 fathoms.
Definition.—Coronida with eight large, partly fenestrated gates; the four upper or lateral gates larger than the four lower or basal gates. Skeleton composed of three latticed complete rings, perpendicular to one another.
The genus Tricyclidium differs from the preceding Tristephanium, its ancestral form, in the development of loose rudimentary lattice-work along the rings, and therefore bears to it the same relation that Plectocoronis does to Eucoronis. It may pass directly over into Dictyospyris.
1. Tricyclidium dictyospyris, n. sp. (Pl. 93, fig. 13).
Sagittal ring ovate, twice as thick as the two other larger rings, which become very thin, thread-like at the lateral junction, and are both slightly violin-shaped, in the middle sagittal plane constricted; the frontal ring larger than the basal. All three rings bear small scattered spines, which are irregularly branched, and by anastomoses of the thread-like branches form small irregular meshes along the rings. The four basal gates are of equal size.
Dimensions.—Height of the frontal ring 0.11, breadth 0.15.
Habitat.—Equatorial Atlantic, Station 347, depth 2250 fathoms.
2. Tricyclidium semantrum, n. sp.
Sagittal ring ovate, smaller than the violin-shaped frontal ring and larger than the elliptical basal ring. All three rings of nearly equal thickness, armed with short irregular branches, which are partly connected, and forming small irregular meshes along the rings. The four basal gates are of different sizes; the two anterior (jugular) gates only half as large as the two posterior (cardinal) gates.
Dimensions.—Height of the frontal ring 0.12, breadth 0.18.
Habitat.—South Atlantic, Station 348, depth 2450 fathoms.
Definition.—Coronida with eight large simple gates of equal size. Skeleton composed of three simple complete rings, perpendicular to one another.
The genus Trissocircus, and the following nearly allied Trissocyclus, differ from the two preceding ancestral genera in the remarkable growth of the four basal gates, which reach the size of the lateral gates. Therefore both hemispheres of the shell (the upper or apical and the lower or basal) here become equal and the basal ring becomes equatorial. Sometimes even all three rings attain the same size, so that it is difficult or impossible to distinguish them. In this curious case the Coronida exhibit a striking resemblance to some Sphæroidea.
Definition.—Sagittal ring smaller than the two other rings, which are both elliptical.
1. Trissocircus lentellipsis, n. sp. (Pl. 93, fig. 10).
All three rings elliptical, of different sizes, smooth, without spines. The sagittal ring is the smallest, but two to three times as thick as the other two rings, which have the larger (transverse) axis common. The smaller (sagittal) axis of the sagittal ring is also the smaller axis of the equatorial ring, whilst the larger (principal) axis of the former is the smaller axis of the frontal ring.
Dimensions.—Height of the frontal ring 0.07, breadth 0.1.
Habitat.—Western Tropical Pacific, Station 224, depth 1850 fathoms.
2. Trissocircus binellipsis, n. sp. (Pl. 83, fig. 6).
Sagittal ring circular, smaller than the other two rings, which are both equal, elliptical, slightly constricted on the poles of the principal and transverse axes. The axis of the circular sagittal ring is the shorter axis of the frontal and equatorial ring, and about half as long as their longer axis. All three rings smooth, without spines.
Dimensions.—Height of the frontal ring 0.08, breadth 0.12.
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.
3. Trissocircus octostoma (Pl. 93, fig. 11).
Sagittal ring circular, smaller than the other two rings, which are both equal, elliptical, distinctly constricted at the poles of the principal and transverse axes. The axis of the circular sagittal ring is the shorter axis of the frontal and equatorial ring, about one-third shorter than their longer axis. All three rings armed with short, irregularly branched spines.
Dimensions.—Height of the frontal ring 0.1, breadth 0.12.
Habitat.—Indian Ocean, Ceylon (Belligemma), Haeckel, surface.
Definition.—All three rings equal, circular.
4. Trissocircus octahedrus, n. sp.
All three rings equal, circular, smooth, their rods cylindrical (in the transverse section circular). From each pole of the three equal axes arises a short conical spine; these six spines correspond to the six corners of a regular octahedron.
Dimensions.—Diameter of all three rings 0.08, thickness 0.006.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
5. Trissocircus globus, n. sp. (Pl. 82, fig. 13).
All three rings equal, circular, thorny; their rods prismatic (in the transverse section triangular), with three sharp dentated edges and scattered branched thorns. From each pole of the three equal axes (which correspond to the three axes of a regular octahedron) arises a bunch of larger spines.
Dimensions.—Diameter of all three rings 0.12, thickness 0.01.
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.
Definition.—Coronida with eight large, partly fenestrated gates of equal size. Skeleton composed of three complete latticed rings, perpendicular to one another.
The genus Trissocyclus differs from its nearly allied ancestral form Trissocircus only in the development of small anastomosing branches along the edges of the rings. The incomplete lattice-work, produced by these anastomoses, partly protects the eight large gates. The three rings are either of equal or of different sizes.
Definition.—Sagittal ring circular, smaller than the other two rings, which are both elliptical.
1. Trissocyclus stauroporus, n. sp. (Pl. 83, fig. 5).
Sagittal ring circular, smaller than the other two equal elliptical rings. On each of the six corners (or crossing points of every two rings) are developed four small pores, forming a cross around the poles of the three axes. All three rings smooth, without spines.
Dimensions.—Height of the frontal ring 0.09, breadth 0.13.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
2. Trissocyclus triaxonius, n. sp.
Sagittal ring circular, smaller than the two other equal elliptical rings. From the edges of all three rings are developed small branches, which by irregular ramification and anastomoses form small irregular meshes along the rings. Similar to Trissocircus octostoma, but with thicker rings; it may be developed from the latter species by connection of the branches which border the rings.
Dimensions.—Height of the frontal ring 0.12, breadth 0.15.
Habitat.—South Pacific, Station 298, depth 2225 fathoms.
Definition.—All three rings equal, circular.
3. Trissocyclus sphæridium, n. sp. (Pl. 93, fig. 12).
All three rings equal, circular, thorny; their rods prismatic, three-sided, with three denticulate edges; the teeth of the lateral edges become branched, and form by anastomoses of the branches small irregular meshes, which partly protect the eight large open gates.
Dimensions.—Diameter of the three rings 0.16, thickness 0.012.
Habitat.—Indian Ocean, Belligemma, Ceylon (Haeckel), surface
Parastephida, Haeckel, 1881, Prodromus, p. 446.
Definition.—Stephoidea with two parallel horizontal rings, an upper mitral and a lower basal ring; both connected by complete or incomplete vertical rings, or by parallel vertical columellæ.