THE EOCENE PERIOD. 



293 



a canal (when the shell is said to be " siphonostomatous ") - 

 this section including the carnivorous and most highly- or- 



Fig. 216. Cardlta planicosta. Middle Eocene. 



gani3ed groups of the class. Not only is this the case, but 

 a large number of the Eocene Univalves belong to types 

 which now attain their maximum of development in the 

 warmer regions of the globe. Thus we find numerous species 

 of Cones (Comis), Volutes ( Valuta}, Cowries (Cyprcza, fig. 218), 



Fi. 217. Typhis titb ; fer, a "siphonosto- 

 matous " Univalve. Eocene. 



Fig. 218. Cy/>ra-a 

 elegans. Eocene. 



Olives and Rice-shells (Ofiva), Mitre-shells (Mitra\ Trumpet- 

 shells (Triton), Auger-shells (Terebra), and Fig-shells (Pyrula). 

 Along with these are many forms of Plcurotoma, Itostdlaria, 

 Spindle-shells (Fusus), Dog-whelks (Nassa\ Murices, and many 

 round-mouthed (" holostomatous ") species, belonging to such 

 genera as Turritdla, Ncrita, Natica, Scalaria, &c. Hie genus 

 Cerithium (fig. 219), most of the living forms of which are 

 found in warm regions, inhabiting fresh or brackish waters, 

 undergoes a vast development in the Eocene period, where it 



