British species of Cyclas and Pisidium. 305 



I can no where find any allusion to this species, which though 

 similar to the two last in the general form of the shell, may at once 

 be distinguished from both, if attention be paid to the animal. I have 

 examined upwards of an hundred specimens from different localities, 

 and in every instance it has preserved its characters. Its chief pecu- 

 liarity consists in the formation of the siphonal tube, which is regularly 

 funnel-shaped, with the aperture very patulous, somewhat plaited at 

 the margin, and more or less crenate. — These appearances are not always 

 obvious, unless the siphon is protruded by the animal to its utmost 

 extent : the mouth of the tube, which is rendered very dilatable in 

 consequence of the plaits, then becomes fully expanded, and the irregu- 

 larity of its partially reflexed margin is rendered distinctly visible. — 

 The shell also, which is subject to scarcely any variation, is remarkable 

 for its extremely glossy hue and cleanly appearance, rarely presenting 

 any of that foulness with which the last and following species are so 

 often incrusted, although found inhabiting the same ditches ; from which 

 circumstance it would seem to follow, that in the case of those species, 

 this is due to something more than a mere extraneous deposit from 

 the surrounding soil. It may also be distinguished by a few peculiar 

 striae drawn with great regularity across the umbones near the apex of 

 each valve, and cut rather more deeply than the rest. This character, 

 however, will not be seen without a close examination. It is most 

 visible when the animal is alive and the glossiness of the shell remains 

 unimpaired ; but even then it is sometimes necessary that this should 

 be held to the light and turned in different directions, in order that 

 the eye may catch the appearance in question. It is, however, more 

 or less obvious in every specimen that I have seen. 



This species is widely dispersed throughout Cambridgeshire, in- 

 habiting various situations, though seemingly partial to clear water. It 

 is however seldom found in any great plenty. — I have also met 



Vol. IV. Part II. Qq 



