THE EOCENE PERIOD. 



293 



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

 this section including the carnivorous and most highly- or- 



Cardita planicosta. Middle Eocene. 



ganised 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 (Cojius), Volutes {Voluta), Cowries {Cypi^cea, fig. 218), 



Fig. 217. — Typhis tubifer, a "siphonosto- 

 matous " Univalve. Eocene. 



Fig. 218. — CyprcBa 

 elegans. Eocene. 



Olives and Rice-shells {Oliva), Mitre-shells (Mitra), Trumpet- 

 shells [TritoJi), Auger-shells [Terebj-a), and Fig-shells {Pyrula). 

 Along with these are many forms of Fleurotoma, Rostellaria^ 

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

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

 genera as Tiirritella^ Nerita, JVatka, Scalaria, &c. The 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 



