15. Dictyospyris hexastoma, n. sp.
Shell nut-shaped, tuberculate, with deep sagittal stricture. Pores small, irregular, roundish. Three pairs of larger pores on each side of the ring. Basal plate with six large pores; the middle pair (cardinal) twice as large as the anterior (jugular) and the posterior (cervical).
Dimensions.—Shell 0.08 long, 0.12 broad.
Habitat.—Fossil in Barbados.
16. Dictyospyris enneastoma, n. sp.
Shell ellipsoidal, smooth, without external sagittal stricture, but with an internal free sagittal ring. Pores small and numerous, regular, circular. No larger annular pores. Basal plate with nine pores, three larger interradial alternating with three pairs of adradial.
Dimensions.—Shell 0.07 long, 0.11 broad.
Habitat.—South Pacific, Station 297, depth 1775 fathoms.
17. Dictyospyris polystoma, n. sp.
Shell nut-shaped, mammillate, with distinct sagittal stricture. Pores small and numerous, irregular, on each side of the ring three to five times as large as on the lateral sides. Basal plate with twelve large pores (four central and four alternate pairs of peripheral).
Dimensions.—Shell 0.1 long, 0.14 broad.
Habitat.—Tropical Atlantic, Station 338, depth 1990 fathoms.
Family LIII. Tholospyrida, n. fam.
Definition.—Spyroidea with a galea, but without thorax; the shell being composed of the bilocular cephalis and of an aboral cupola or galea arising from its coryphal face.
The family Tholospyrida differs from the preceding Zygospyrida, its ancestral group, in the development of a galea, i.e., a fenestrated hemispherical or dome-shaped cupola, which covers the upper face of the cephalis like a cap.
Only three species of this family have been hitherto described: Pylospyris (or Spyridobotrys) trinacria, figured in my Monograph (1862), Pylospyris (or Lithopera) denticulata, figured by Ehrenberg (1872), and Lophospyris (or Ceratospyris) acuminata, figured by Hertwig (1879). Fourteen new species have been found in the collection of the Challenger, which we dispose here among five genera. These may be derived from corresponding genera of Zygospyrida by the development of a galea.
