GASTBOPODA 545 



greenish ; tentacles long and slender with eyes at their outer base ; snout 

 prolonged; ctenidium bipectinate, long, exposed; animals hermaphro- 

 ditic: the temperate regions of the globe, in rivers, ponds, and lakes; 



1 genus. 



Valvata 0. F. Miiller. With the characters of the family: about 

 6 American species, 3 being on the Pacific slope. 

 Key to the species of Valvata here described: 



Oi Whorls of shell rounded V. sincera 



02 Whorls keeled. 



&i Apex elevated Y. tricakinata 



63 Apex not elevated V. bicarinata 



V. sincera Say (Fig. 849). Shell conical and depressed, with 3 or 



4 whorls; spire very low; lowest whorl very large, rounded; aperture 



round, beneath the rest of the shell; surface shining and brownish in 



color ; length 2.5 mm. ; width 4.5 mm. : Canada 



/^'O^ yjCS^^j^ and Alaska and the northern states towards the 



C-:^^--^^^ \— c^^T^ north; in lakes and sluggish streams. 



Fig. 849 Fig. 850 V. tiicarinata (Say) (Fig. 850). Shell 



Fig. 8^9-yalvata sincera depressed, thin, shining, whitish or greenish 



i^?arfnafrfBfker7.^°^'"*'' ^^ ^olor, with an elevated spire flattened at 



the apex; whorls 3 or 4, with deep sutures, 

 and with 1 to 3 prominent keels on the outer surface; length and width 

 4 mm. : northern states, south to Iowa ; very common. 



V. bicarinata Lea. Shell discoid, the spire not elevated, and with 

 no more than 2 keels; length 3.5 mm.; width 5 mm..: northern states. 



Family 9. AMPULLARIIDAE. 



Shell with a low spire and a large lower whorl and aperture; snout 

 divided into two long tentacular lobes; tentacles long and slender, with 

 eyes on short stalks at their outer base; mantle with a long siphon on 

 the left side; respiratoiy cavity divided by a partition, the left acting 

 as a pulmonary sac, the right containing a very large ctenidium: numer- 

 ous species; in fresh water, principally in tropical regions. 



Ampullaria Lamarck. With the characters of the family; um- 

 bilicus widely open: 150 species. 



A. depressa Say. Shell with 4 whorls, yellowish in color, with 

 numerous revolving brown or greenish bands; 37 mm. long and wide: 

 Florida and Georgia, in rivers and lakes. 



Family 10. CERITHIIDAE. 



Shell elongate, with a tall spire and a ridged or tuberculated sur- 

 face; aperture channeled in front, forming a short canal, and usually 



