106 Rev. L. Jenyns on the smaller British species of Pisidium. 



As I have here proposed to unite Pisidium Henslowianum and 

 P. pulchellum of my monograph under one species, giving it the 

 name first mentioned, — if it be thought desirable still to retain 

 a name for that variety which is so peculiarly distinguished by 

 the umbonal appendages, — it might be called var. appendiculata, 

 which was the name given to it by Dr. Leach, after he had 

 transferred that of Henslowiana to the variety of the P. amnicum 

 above alluded to. 



Pisidium pusillum. — Mr. Watson of Ackworth sent me, along 

 with the P. Henslowianum, specimens of a shell from that neigh- 

 bourhood, not to be distinguished from P. pusillum, except by 

 their far greater size, some of the individuals measuring 2 J lines 

 in length. I have received others from Suffolk of the same size, 

 but rather more tumid, and nearly If line in thickness; form 

 exactly similar. 



Other specimens sent me from Preston Moor by Mr. Gilbert- 

 son agree likewise exactly in form with the P. pusillum of my 

 monograph, but have the striae deeper cut in proportion to their 

 larger size, which exceeds that of even the Ackworth and Suffolk 

 specimens, some being %\ lines in length, but they are not quite 

 so tumid as the latter. 



Specimens from Guisborough, likewise sent by Mr. Watson, 

 are nearly 2f lines in length, but are slightly more compressed 

 in proportion to their size than those from Preston Moor, though 

 in other respects similar ; and some of these Guisborough ones 

 are scarcely to be distinguished, either in form or colour, from 

 the P. cinereum of Alder (judging from a series of specimens 

 kindly sent me, some years back, by that gentleman himself), 

 except that the P. cinereum is rather more compressed still. 



From all the above, I am inclined to think that the P. pusil- 

 lum and P. cinereum are not distinct ; though never having seen 

 the animal, or noticed the habits of the latter, I would not wish 

 to be considered as speaking positively on this point. I observe, 

 too, that Forbes and Hanley, in their 'British Mollusca/ men- 

 tion a variety of P. cinereum which is " rather more ventricose, 

 and produced at the unbones," whereby the species is brought 

 into close approximation with some of the varieties of P. pusil- 

 lum above alluded to. 



Pisidium obtusale and P. nitidum. — Of these two species I 

 have never received specimens from any of my correspondents, 

 unless a few doubtful individuals, sent from Aberdeen by the 

 late Prof. Macgillivray, be referable to the P. obtusale. Hence 

 I conclude that they are much less generally distributed than 

 the other species of this genus. Having, however, occasionally 

 had shells sent me which were erroneously supposed to belong 

 to the species in question, I must again caution collectors against 



