British species of Cyclas and Pisidium. 299 



Cyclas lacustris, Alder in Trans. Nat. Hist. Soc. Newcast. 1. 40. 

 Brit. 3Ius. 3ISS. 

 Var. 7. 



Testa orbiculato-rhombea, minus compressa, subdiaphana, rufescente; 

 natibus nigricantibus, minus prominulis. 



Cyclas stagnicola, Leach (olim.) 



C. calyculata, (2), Lamarck, 5. 559. 

 Animal (in Var. /3) album, tubis siphonalibus concoloribus ; hi valde elon- 



gati, nunc superiore, nunc inferiore alium longitudine superante, 



quoad formam fere ut in specie prascedenti. 

 Testa quam maxime variabilis, rhombea, orbiculato-rhombea, sub-ovalis, 



vel exacte orbicularis ; plus minusve compressa, tenuis, diaphana, 



levissime striata; plerumque cajrulescenti-alba, zona, marginali lutes- 



cente; — interdum fusco-rufescens, minus diaphana, apice nigricanti: 



nates acutiusculee, tuberculosa?, in a et /3 prominentes, interdum etiam 



subinflexa?: ligamentum inconspicuum. 



I feel satisfied that the above described shells are only varieties of 

 one species, and all referable to the C. calyculata of Draparnaud. One 

 of them is the C. lacustris of the British Museum, and also of Mr Alder, 

 as I have been enabled to ascertain from specimens kindly forwarded 

 to me by that gentleman. Var. 7, which only differs from the last in 

 having the tubercles on the beaks not quite so prominent and well 

 defined, I believe to be the variety, as I have already stated, originally 

 sent to Lamarck by Dr Leach under the name of C. stagnicola. Mr Alder 

 was of opinion that his shell was the C. lacustris of Draparnaud, but 

 as Lamarck has referred the variety last mentioned (which differs so 

 little from it) to the present species, and as he was acquainted with 

 botli the C. calyculata and lacustris, there can be little doubt that this 

 last is distinct from either of the above. — Indeed I have never seen 

 any British shell exactly answering to the C. lacustris of the continental 



Pi'2 



