PISIDIUM. 127 



the validity of its specific separation must rest rather upon 

 the animal than the shell. Nevertheless, when well deve- 

 loped, its umbonal sulci will afford to the accurate observer 

 a ready means of discriminating it : these, however, de- 

 mand a most searching examination for their discovery. 

 The general shape is of a rounded oval ; it is slightly more 

 convex than the preceding species and broader in propor- 

 tion to it ; is highly lustrous and rarely, if ever, clothed like 

 it with a rusty or muddy coating. The general surface 

 is only obsoletely striated at intervals, but the umbonal 

 region is concentrically traversed with a few regular sulci, 

 whose interstices often appear like elevated striulee. The 

 umbones themselves are rather obtuse, projecting but little 

 above the dorsal line. The larger examples are an eighth 

 of an inch in length, and not much inferior in breadth. 



The animal, according to Jenyns, is white ; its siphon 

 short and funnel-shaped, with a patulous aperture, the 

 margin of which is more or less crenated or plicated. 



Mr. Jenyns obtained his original specimens from ditches 

 in Battersea Fields, and other parts of Surrey, as well as 

 from various spots in Cambridgeshire, where (he observes) 

 it is widely dispersed, though seldom plentiful, and is 

 seemingly partial to clear water. Mr. Jeffreys has ob- 

 tained it from Clumber Lake in Nottinghamshire, and at 

 Sandwich in Kent ; Mr. Bean from Scarborough ; Mr. 

 A. Hancock in Northumberland, and Mr. W. Backhouse 

 near Darlington. 



In Wales it has been found at Oxwich near Swansea, 

 and Tenby and Manorbeer in Pembrokeshire (Jeffreys). 



It is generally distributed in Ireland, and abundant in a 

 cold turfy deposit conveyed by a mountain-stream to a 

 pond at Wolfhill, near Belfast, and on the Utricularla 

 vulgaris growing in stagnant pools near that town ; Lough 



