460 



MESOZOIC TIME — REPTILIAN AGE. 



omata, Lower Oolite, are characteristic forms. The Gasteropods with an entire 

 aperture are still far the most abundant species ; but a few genera with a beak 

 exist, and the Purpuroidea (near the modern Purpura) is one example. Except 

 in the great predominance of species with the aperture entire, the Gasteropoda 

 have generally a modern aspect : among them there are the genera Bulla, Ptero- 

 cera, Cerithium, Fusus, Nerita, Patella ?, and others. 



(c.) Cephalopoda. — Tetrabranchs. — Fig. 730, Ammonites Humphreysianus, Lower 

 Oolite; A. Parkinsoni, Lower Oolite; A. cordat us, Middle Oolite j fig. 731, A.Jason 

 Middle Oolite; A. refractus, Middle Oolite; also species of Aneyloceras and 

 Toxoceras (see figs. 787, 789). 



Dibranchs. — Belemnites hastatm, Oxford Clay. Fig. 732, Acanthoteuthis anti- 

 quus, Oxford Clay. Also species of the Calamary and Sepia families, as Cocco- 



Figs. 730-732. 



31 



Cephalopods.— Fig. 730, Ammonites Humphreysianus; 731, A. Jason; 732, Acanthoteuthis 

 antiquus (X%)- 



teuthis of the latter. The osselet in the Sepia group is calcareous instead of 

 membranous (p. 156). 



