VALVATA. 19 



Animal Muzzle produced ; cylindrical elongated tentacles, 

 with eyes at the hinder extremities. 



V. PISCINALIS. Mutter. PL IV, fig. 4. 



Somewhat globular, with an elevated deeply sutured spire of three 

 whorls, above the last volution ; umbilicus a whitish colour. 



The two species of Valvata differ much in general 

 appearance, the one being comparatively long and spi- 

 ral, the other discoid and depressed. 



Shell nearly a quarter of an inch in length and the 

 same in breadth. 



Hob. Canals, streams, and ponds. It is generally 

 distributed all over the British Isles, though by no 

 means common in some districts. 



V. CRISTATA. Mutter. PL IV, fig. 3. 



Discoid, flat ; spire level or somewhat below the last volution. 



The whorls are cylindrical, three in number and 

 deeply saturated. The shell is thin and of a light 

 horn colour ; about one tenth of an inch in diameter ; 

 somewhat resembles a PlanorUs, but is readily distin- 

 guished by the operculum. 



Hob. Ditches and ponds in many parts of Britain, 

 and where found they are usually plentiful. Distri- 

 buted all over Ireland. 



LITTORINIDJE. 



ASSIMINIA. Gray. 

 Shell Spiral, conical, smooth. Operculum corneous. 



Animal Head, muzzle-shaped; two tentacles with eyes at 

 the extremities. 



A. GRAYANA. Jeffreys. PI. IV, fig. 2, and PL 

 VIII, fig. 2. 



Ovate ; of a brown colour ; mouth of the animal elliptical. 



This shell is never found except in brackish water. 

 The spire which consists of several whorls is rather 

 acute. It is about a quarter of an inch in length. 



Hab. The mouths of rivers amongst confervce, &c. 

 c 2 



