280 



HISTORICAL PALAEONTOLOGY. 



Limestone, and the Pisolitic Limestone of France, we meet 

 with a number of carnivorous (" siphonostomatous ") Uni- 

 valves, in which the mouth of the shell is notched or pro- 

 duced into a canal. Amongst these it is interesting to 

 recognize examples of such existing genera as the Volutes 

 (Valuta, fig. 200), the Cowries (Cyprcca}, the Mitre-shells 

 (Mitra}, the Wing-shells (Strombus), the Scorpion-shells 

 (Pleroceras}, &c. 



Upon the whole, the most characteristic of all the Creta- 

 ceous Molluscs are the Cephalopods, represented by the remains 

 of both Tetrabranchiate and Dibranchiate forms. Amongst the 

 former, the long-lived genus Nautilus (fig. 201) again reap- 

 pears, with its involute shell, its capacious body-chamber, its 

 simple septa between the air-chambers, and its nearly or quite 

 central siphuncle. The majority of the chambered Cephalo- 

 pods of the Cretaceous belong, however, to the complex and 

 beautiful family of the Ammonitida , with their elaborately 

 folded and lobed septa and dorsally-placed siphuncle. This 



Fig. 201. Different views of Nautilus Danicug. Faxoe Limestone 

 (Upper Cretaceous), Denmark. 



family disappears wholly at the close of the Cretaceous period ; 

 but it approaching extinction, so far from being signalized by 

 any slow decrease and diminution in the number of specific 

 or generic types, seems to have been attended by the develop- 

 ment of whole series of new forms. The genus Ammonites 

 itself, dating from the Carboniferous, has certainly passed its 

 prime, but it is still represented by many species, and some of 

 these attained enormous dimensions (two or three feet in 

 diameter). The genus Ancyloceras (fig. 202), though likewise 

 of more ancient origin (Jurassic), is nevertheless very charac- 



