118 NEW-YORK FAUNA — MOLLUSCA. 



GENUS VALVATA. Muller. 



Animal with a distinct head, elongated with a proboscis. Tentacles very long, approximate, 

 cylindrical, obtuse : eyes sessile, behind their bases. Foot bilobed in front. Gills long, 

 pectiniform, more or less exsertile. Cavity widely patulous, and furnished on the right of 

 its lower margin with a long appendix resembling a third tentacle. The male organ retrac- 

 tile into the breathing cavity. Inhabiting fresh water. Shell discoid or conoid: whorls- 

 cylindrical, loosely cohering ; aperture circular, its margin sharp, entire ; opercle circular, 

 horny. 



Valvata tricarinata. 



PLATE VI. FIG. 130. A. B. 



(STATE COLLECTION.) 



Cyclostoma tricarinata. Say, Nicli. Ency. Acad. Nat. Sc. Vol. 1, p. 15. 

 Valvata id. Adams, American Journal of Science, Vol. 40, p. 267. 



V. id. Gould, Invertebrata of Mass. p. 225, fig. 156. 



Description. Shell small, thin, depressed. Whorls three, flattened at the summit ; the 

 body-whorl with three revolving keels, the others with but two. Suture deeply impressed ; 

 aperture circular, oblique, modified by the keels ; umbilicus large, patulous, and exliibiting 

 all the volutions to the summit. 



Color. Brownish white, often pearly, occasionally greenish. 



Height, 0-1. Diameter, 0-07. 



Found in many streams and ponds throughout the State. 



Valvata unicarinata. 



PLATE VI. FIG. 129. 

 (STATE COLLECTION.) 



Description. Shell small ; apex depressed. Whorls three or four, impressed with minute 

 incremental striae, all flattened above, and bounded by a revolving rib or keel, which in the 

 younger individuals ascends to the summit. Aperture circular, nearly vertical, scarcely mo- 

 dified by the keel. Opercle corneous, thin, with concentric striae : umbilicus wide, profound, 

 exhibiting all the volutions. 



Color. Milky bluish white ; apex often tinged with rufous. 



Height, • 1 . Diameter, • 1 5 . 



These dimensions are from one of the largest size, obtained from Lake Champlain, where 

 they are very abundant, and from the Erie canal. It is allied to the preceding, and forms 



