Family XV. Cyphinida, Haeckel (Pl. [39], figs. 11-19).
Cyphinida, Haeckel, 1881, Prodromus, p. 462.
Definition.—Prunoidea with ellipsoidal twin-shell, divided by an equatorial stricture into two communicating hemiellipsoidal or hemispherical chambers; this external twin-shell (cortical shell) is either simple or double, and encloses one or more internal concentric shells (medullary shells). Central capsule ellipsoidal, commonly with an equatorial constriction.
The family Cyphinida have the same characteristic twin-form of the cortical shell as the Artiscida, but differ from them in the presence of a simple or double internal medullary shell, connected with the cortical shell by radial beams. The fenestrated shell is therefore composed of two or more concentric shells as in the Druppulida, but differs from these in the ring-like equatorial constriction.
The Medullary Shell, in the middle of the central capsule, is either single or double, composed of two concentric shells. As in the Druppulida, the form of the medullary shells is either spherical (Pl. [39], fig. 12a) or lenticular, compressed from both poles of the main axis (Pl. [39], fig. 18a); sometimes the inner medullary shell is spherical, the outer lenticular.
The Radial Beams, which connect the medullary shell with the equatorial constriction of the cortical shell, lie either all in the equatorial plane (Pl. [39], fig. 11) or near it on both sides (Pl. [39], figs. 12a, 18a).
The Cortical Shell is commonly simple (Pl. [39], figs. 12, 18), sometimes composed of two concentric shells (Pl. [39], fig. 13), rarely of three. As in the Artiscida, also in the Cyphinida, from both poles of the main axis solid spines or hollow fenestrated tubes are often developed (Pl. [39], figs. 14, 16-18).
The Central Capsule of the Cyphinida (Pl. [39], fig. 13) is of the same form as in the Artiscida, generally ellipsoidal, but with an equatorial ring-like stricture, which divides it into two equal halves. It encloses the simple or double medullary shell, and is perforated by the radial beams starting from this. From the inner surface of the surrounding cortical shell it is separated by a thicker or thinner jelly-layer, the calymma. (Compare also Taf. xxii. fig. 14 of my Monograph, 1862.)
Synopsis of the Genera of Cyphinida.
| Cortical shell without peculiar spines or hollow fenestrated tubes on both poles of the main axis. |  | Cortical twin-shell simple |  | Medullary shell simple, | 155. Cyphanta. |
| Medullary shell double, | 156. Cyphonium. | ||||
| Cortical twin-shell double or triple; medullary shell double. | | Cortical shell double, | 157. Cypassis. | ||
| Cortical shell triple, | 158. Cyphocolpus. | ||||
| Cortical shell simple, with peculiar spines or hollow fenestrated tubes on both poles of the main axis. | | Two opposite polar spines (or bunches of spines). | | Medullary shell simple, | 159. Cyphinus. |
| Medullary shell double, | 160. Cyphinidium. | ||||
| Two opposite hollow fenestrated polar tubes. | | Medullary shell simple, | 161. Cannartiscus. | ||
| Medullary shell double, | 162. Cannartidium. |