PLANORBIS. 37 



fusion in Dringhouses Bog, near York" (Hey), J.C., 

 Oct. 1879 ; it has also been found in Nottinghamshire, 

 and in Ireland, in Co. Tipperary, but it is not a com- 

 mon species. 



It is rather active, and when crawling carries its 

 shell in the same plane with its foot. 



It breeds in August, laying only from three to eight 

 eggs, which are enclosed in a roundish, transparent, 

 amber-coloured capsule. The young are excluded in 

 from ten to twelve days. 



2. P. NI'TIDUS,* MULLER. PL. IV. 



Body rather transparent, reddish-grey or ash-colour with a 

 yellowish tinge, somewhat darker underneath, marked with 

 numerous very fine dark grey specks ; tentacles filiform, extremely 

 slender, pointed at their tips, transparent, pale reddish-grey ; 

 eyes prominent ; foot short, obtuse in front, narrowing slightly 

 towards the tail which is bluntish at its extremity. 



Shell quoit-shaped, much depressed, very thin and glossy, 

 iridescent, greyish or pale yellowish horn-colour, sometimes 

 faintly tinted with red ; with fine, indistinct striae in the line of 

 growth, and sometimes microscopically striate spirally ; epidermis 

 very thin ; periphery sharply keeled ; whorls 4-5, the last but 

 one about half covered by the body whorl which slopes gradually 

 outwards ; spire depressed, but much less so than that of P. 

 lineatus ; suture deepish ; mouth as in the last species but more 

 compressed ; umbilicus small, shallow. 



Inhabits lakes, ponds, and marshes in most parts of 

 Great Britain, attaching itself to and feeding upon 

 aquatic plants. It is a timid and inactive species ; the 

 eggs, in number from three to five (rarely six), are 

 roundish or slightly oval, transparent, and somewhat 

 depressed. 



* Shining. 



