British species of Cyclas and Pisidium. 303 



Var. y. 



Striis profundius incisis. 



Animal album ; tubo siphonali brevi, nunc cylindraceo, nunc subconico, 

 margine integerrimo; pede testam longitudine paul6 superante. 



Testa variabilis, plerumque orbiculato-ovalis, interdum suboblonga mar- 

 gine dorsali recto, vix inagquilateralis ; prascedenti multo magis com- 

 pressa, marginibus acutis ; sajpius extranea rubigine obtecta, qua remota, 

 apparent striae subtilissimas, non nisi oculo armato conspiciendse ; in 

 var. 7. nitida, striis distinctis, profundius incisis : umbones subdepressi, 

 parum prominuli, interdum subacuti. 



This species appears to be the Cyclas pusilla of Turton, whose 

 description and figure in his " British Bivalves," apply with tolerable 

 exactness. Specimens also of that shell which I received some time 

 since from the Rev. R. T. Lowe, with the assurance that they were 

 authentic specimens originally from Dr Turton himself, agree with mine 

 in every essential particular, although more compressed, and with the 

 umbones not quite so obtuse and prominent. Nevertheless, I am inclined 

 to think that this name has been occasionally applied to more than 

 one species, particularly to some of the varieties of P. pulchellum here- 

 after to be described, which I have received from one or two collectors 

 as the shell above-mentioned. I likewise consider this species as sy- 

 nonymous with the Cyclas fontinalis of Nilsson, although I entertain 

 some doubts as to its identity with the C. fontinalis of other conti- 

 nental authors. Draparnaud especially has comprised under this name 

 two varieties differing so materially in size, as to render it hardly pro- 

 bable that they belong to the same species. 



Pisidium pusillum is distinguished from P. obtusale by the shell being 

 much more compressed than in that species, and by the margins of 

 the valves meeting at an acuter angle: the hinge is also nearly central. 



