| Cortical shell without polar appendages (neither solid spines nor hollow tubes at the poles of the main axis). | ||||||||
| Cortical shell simple, ellipsoidal. | ||||||||
| Medullary shell simple. | ||||||||
| Surface smooth, | ||||||||
| 131. Druppula. | ||||||||
| Surface spiny, | ||||||||
| 132. Druppocarpus. | ||||||||
| Medullary shell double. | ||||||||
| Surface smooth, | ||||||||
| 133. Prunulum. | ||||||||
| Surface spiny, | ||||||||
| 134. Prunocarpus. | ||||||||
| Cortical shell composed of two or more concentric shells. | ||||||||
| Medullary shell double. | ||||||||
| Surface smooth, | ||||||||
| 135. Cromyodruppa. | ||||||||
| Surface spiny, | ||||||||
| 136. Cromyocarpus. | ||||||||
| Two opposite solid spines, arising from the poles of the main axis. | ||||||||
| Cortical shell simple, ellipsoidal. | ||||||||
| Medullary shell simple. | ||||||||
| Both polar spines equal, | ||||||||
| 137. Lithatractus. | ||||||||
| Both polar spines unequal, | ||||||||
| 138. Druppatractus. | ||||||||
| Medullary shell double. | ||||||||
| Both polar spines equal, | ||||||||
| 139. Stylatractus. | ||||||||
| Both polar spines unequal, | ||||||||
| 140. Xiphatractus. | ||||||||
| Cortical shell composed of two or more concentric shells; medullary shell double; both polar spines equal, | ||||||||
| 141. Cromyatractus. | ||||||||
| Two opposite hollow fenestrated tubes, arising from the poles of the main axis. | ||||||||
| Cortical shell simple, ellipsoidal. | ||||||||
| Medullary shell simple, | ||||||||
| 142. Pipetta. | ||||||||
| Medullary shell double, | ||||||||
| 143. Pipettaria. | ||||||||
Genus 131. Druppula,[[170]] n. gen.
Definition.—Druppulida with simple ellipsoidal, cortical shell, and simple medullary shell, without spines or polar tubes.
The genus Druppula, as the simplest form of the Druppulida, may be regarded as the common ancestral form of this subfamily. It may be derived phylogenetically either from Carposphæra by prolongation of one axis, or from Cenellipsis by duplication of the fenestrated shell. The outer (or cortical) shell is always more or less ellipsoidal; the inner (or medullary) shell also is sometimes ellipsoidal, sometimes spherical. Both shells are concentric, connected by a variable number of radial beams. Compare Haliomma oblongum, Harting, 1863, L. N. [18], p. 15, pl. 2, fig. 42.
Subgenus 1. Druppuletta, Haeckel.
Definition.—Pores of the cortical shell regular, hexagonal, or circular.
1. Druppula drupa, n. sp.
Cortical shell thin walled, with smooth surface and regular network; both its axes bear the proportion of 4 : 3. Pores regular, hexagonal, three times as broad as the bars; twelve to fifteen on the half equator. Medullary shell spherical, about one-third as broad as the cortical shell.
Dimensions.—Major axis of the ellipsoidal cortical shell 0.1 to 0.12, minor axis 0.08 to 0.09; pores 0.06, bars 0.02; diameter of the medullary shell 0.03.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms; also fossil in Barbados.