British species of Cyclas and Pisidium. 297 



casionally ascend the sides of the vessel in which it is kept, and 

 during locomotion I have observed that the tubes are either partially 

 exserted, or entirely concealed. 



The variety /3 agrees with the series of specimens in the British 

 Museum named by Dr Leach C. stagnicola. I am inclined to believe 

 also that it is the same with the Tellina stagnicola of Mr Sheppard 

 as the remarks made by this latter gentleman with respect to the 

 peculiar appearance of the umbones, apply very exactly; and it is 

 particularly stated that he first received specimens from Dr Leach 

 under the above name. Nevertheless I feel satisfied that it is a mere 

 variety of C. cornea, as the animal is exactly the same in the two in- 

 stances; and with regard to the peculiarity of the shell, many interme- 

 diate specimens may occasionally be met with. It is necessary, however 

 to mention, that the name of stagnicola appears to have been applied 

 by Dr Leach at different times to two distinct species. The series of 

 shells at present so named in the British Museum, are certainly the 

 variety of C. cornea now under consideration ; but I possess two spe- 

 cimens of a shell which came originally from Dr Leach, and which 

 have the name of stagnicola under them in that gentleman's own hand- 

 writing, evidently belonging to the C. calyculata of Draparnaud, (Var. 7 

 of this paper,) and I am inclined to think that it was this latter shell 

 which was formerly sent by the Doctor to Lamarck under the above 

 name, and considered by that author to be a mere variety, not of 

 C. cornea, but of the species last mentioned. 



Other varieties of C. cornea, besides those above-mentioned, are not 

 uncommon. Occasionally the shell exhibits gibbosities, and the maro-j,, 

 becomes very obtuse : at other times the valves are much compressed, 

 and their margins meet at an acute angle. In the fens of Cam- 

 bridgeshire, a small variety is not unfrequent in the turf pits almost 

 globular, and somewhat similar both in size and shape to a pea. 

 Vol. IV. Part II. p, 



