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.—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 (Conus), Volutes ( Voluta), Cowries (Cyprea, fig. 218), 
Fig. 217.—Typhis tubifer, a ‘‘siphonosto- Fig. 218. — Cyfrea 
matous ” Univalve. Eocene. elegans. Eocene. 
Olives and Rice-shells (OZva), Mitre-shells (J/tra), Trumpet- 
shells (Z7zfon), Auger-shells (Zerebra), and Fig-shells (Pyru/a). 
Along with these are many forms of Pleurotoma, Rostellaria, 
Spindle-shells (Fusws), Dog-whelks (Vassa), Murices, and many 
round-mouthed (“ holostomatous ”) species, belonging to such 
genera as Turritella, Nerita, Natica, 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 
