British species of Cyclas and Pisidium. 309 



but subsequently changed the name to that of Pera appendiculata, 

 reserving the above specific name for another and larger shell. This 

 last having however since proved to be a mere variety of the following, 

 I have restored the name of Henslowianum to the present species, 

 which has indeed already been described under that title by the Rev. 

 It. Sheppard in the LinnEean Transactions. — This shell is so strikingly 

 distinguished by the curious eave-like projection upon the umbones, that 

 it cannot be confounded with any other. In quite young specimens 

 this projection is, as it were, a small wing arising from the middle of the 

 valves, but as the growth of the shell proceeds, this last receiving its 

 increase principally at the basal margin, it appears to mount higher up, 

 until at length in adult individuals it occupies quite the summit of the 

 shell, where it appears like a small ridge or lamina rising up vertically 

 on either side of the hinge. — In other respects this species is very similar 

 to the last ; nevertheless it is always larger. — I have met with it in 

 two or three parts of Cambridgeshire, but it does not appear to be of 

 very general occurrence. Sheppard found it in Suffolk. 



Sp. 6. P. amnicum, Nobis. — Tab. xix. Fig. 2. 



P. testa ovali, ventricosa, profundius sulcato-striata ; umbonibus ob- 

 tusiusculis. 



Long. 5jlin. Alt. 3| lin. Crass. 2§ lin. 



Tellina amnica, Midler, 2. 205. — Gmelin, 3242. — Linn. Trans. 8. 60. 



Dillwyn, 1. 105.— Turt. Conch. Diet. 168. 



rivalis, Maton, in Linn. Trans. 3. 44. /. 13. f. 37, 38. — Donovan. 



t. 64. / 2. 



Cardium amnicum, Montagu, 86. 



Cyclas palustris, Draparnaud, 131. / 10. f. 15, 16. 



Cyclas obliqua, Lamarck, 5. 559. — A r iisson, 99. 



