302 Mr Jenyns's Monograph on the 



scription given by this last author, a little doubt attaches itself to the 

 latter synonym. — The variety /3, also accords exactly with the Cyclas 

 obtusalis of Nilsson. Dr Leach called it Per a gibbet, but I do not feel 

 certain that all the specimens on the board so named in the British 

 Museum are referable to this species. — It occurs not ^infrequently in 

 Cambridgeshire, inhabiting small splashy pools and other stagnant waters, 

 and I have observed that it is often to be found in company with 

 the Physa Hypnorum Drap. It is by far the most active and lively 

 species that I am acquainted with, being always in motion, and re- 

 siding less at the bottom than the rest of this family. It transports 

 itself rapidly along the under side of the surface of the water, and 

 appears to delight much in floating masses of conferva? and other 

 weeds. Dr Leach's specimens came, I believe, from the neighbour- 

 hood of Battersea Fields ; and I have myself also met with it in 

 other parts of Surrey. 



Obs. — The measurements of this species are usually much less than 

 those above given. 

 Sp. 2. P. pusillum, Nobis. — Tab. xx. Fig. 4 — 6. 



P. testa, orbiculato-ovali, compressiuscula, subtilissime striata, vix in- 

 requilaterali ; umbonibus parum prominulis. 



Long. If lin. Alt. l^lin. Crass. 1 lin. 



Tellina pusilla, Turt. Conch. Diet. 167. 



Cyclas pusilla, Turt. Conchyl. Brit. 251. t. 11. / 16, 17-— Turt. Man. 



16./ 7. 



fontinalis, Nilsson, 101 Druparn. 130. /. 10./ 8—11? 



gibba, Alder in Trans. Nat. Hist. Soc. Newcast. 1. 41. 



Euglesa Henslowiana, Leach 3ISS. Brit. Mus. 



Far. (3. 



Umbonibus magis prominentibus. 



