Mr. Alder's Supplement to his Catalogue. 341 



neighbourhood, and has the shell always stronger and the hairs more deciduous than the 

 specimens of H. hispida found in woods. 



CYCLAS. 



C. lacustris (vol. i. p. 40.) 



The Rev. L. Jenyns's opinion that this is a variety of C. calyculata is probably correct. 



PISIDIUM, Pfeiffer. 



This genus has been divided from Cyclas, and is distinguished by its single siphonal 

 tube and inequilateral shell. As the excellent monograph of Mr. Jenyns in the Cambridge 

 Philosophical Society's Transactions must henceforth be referred to as the best authority on 

 these two genera, I have considered it preferable to adopt his names for the following spe- 

 cies published in my former catalogue, and referable to this genus. 



For C.fontinalis (vol. i. p. 41) read P. pulchellum, Jen. 



The kind formerly noticed is var. p. Jen. 



Var. a. Jen. 



In ponds at Tynemouth and Ouseburn. 



This variety I believe Mr. Jenyns now considers to be a distinct species, but as he has not 

 published it as such, I shall not venture to characterise it. 



Var. h Jen. 



In a pond on Ryton Haughs. 



For C. gibba (vol. i. p. 41) read P. pusillum, Jen. 



For C. obliqua (vol. i. p. 41) read P. amnicum, Jen. 



P. cinereum. 



Animal, white ; with the siphonal tube very short, broad and flat, truncated at the end 

 and seldom protruded much beyond the edge of the shell. Shell of a greyish or cinereous 

 hue, rather compressed, of an oval form, finely striated, and with two or three deep sulca- 

 tions, forming darker zones across the shell ; margins of the valves meeting at a rather 

 acute angle; umbones obtuse, and not much produced; sometimes slightly capped, as in 

 Cyclas calyculata. Length, a little above 2 tenths of an inch; height, If tenths; thick- 

 ness, \\ tenth. 



Plentiful in a pond on the sea banks at Castle Eden. 



Var. cc. more ventricose, and produced at the umbones. 



In a ditch near Brandling Place, Newcastle. 



This species may generally be readily distinguished from others of the genus by its more 

 compressed and oval form, and its cinereous colour. It is the largest of the minute spe- 

 cies. 



VOL. II. 3 s 



