146 



THE MIDDLE PAST. 



gonia, Venus, and many others whose specific forms are new 

 and peculiar to the period ; while gasteropods, like natica, 



1, Pecten ; '2, Terebratula ; 3, Gervillia ; 4, Ostrea ; 5, Plagiostcma ; 6, Inoceramus ; 

 7, Radiolites ; 8, Eippurites ; 9, Cinulia. 



llttorina, cerithium, rostellaria, solarium, pleurotomaria, 

 and others, mark a busy sea-shore of herbivorous and car- 

 nivorous activity. The cephalopods, though numerically 

 fewer than in the lias and oolite, now appear in strange and 

 fantastic forms. Hitherto the chambers of the shell-clad 

 genera were either simply straight, like the orthoceras, or 

 coiled on the same plane, like the nautilus and ammonite. 

 Now, along with the nautilus and ammonite we have them 

 bent like a hook (hamites), curved like the prow of a skiff 

 (scaphites), incurved like a crosier (ancyloceras), curled 

 like a ram's horn (crioceras\ twisted round a straight axis, 



