FAMILY CARDIACEA. 



241 



and used their long foot as an organ of progression, by extending 

 it to its full length. ; and after attaching its point to the bottom of 

 the vessel like a leech, they drew up their shell to it." 



5. Cyclas lacustris. Lake Cyclas. 



Shell ; somewhat squarely orbicular or rhombic, very thin, but little 

 ventricose, light ash-horny substance, nearly 

 equilateral, sides somewhat compressly expanded 

 at the margin, posterior side rather the larger ; 

 umboes nearly central, rather prominent, capped 

 with the calyculate shell of the young fry. 



Tellina lacustris, Midler (1774), Verm. Hist, part ii. p. 204 

 (not of Draparnaud). 



Cardium lacustre, Montagu (1803), Test. Brit. p. 89. 



Cyclas calyculata, Draparnaud (1805), Hist. Moll. p. 130. 

 pi. x. f. 14, 15 (not of C. B. Adams). 



Cyclas lacustris, Ferussac (1807), JEss.Meth. Conch, p. 128. 

 no. 4 (not of Draparnaud) . 



Tellina tuberculata, Alten (1812), Syst. Urol, und Fluss-Conch. p. 4. pi. i. f. 1. 



Tellina tenera, Schrank (1814), Gdrtn. Ann. Meth. p. 316. no. 2. 



Cyclas Ryckholtii, Normand (1844), Not. Nouv. Cycl. p. 7. f. 5. 



Cyclas Terveriana, Dupuy (1849), Cat. Extram. Test. no. 87. 



Splicerium lacustre, Ryclcholtii, and Terverianum, Bourguignafc (1853), Rev. 

 Soc. Cuv. p. 345. 



Sphcerium Brochonianum, Bourguignat (1854), Mem. Soc. Sci. Bord. vol. i. 



Spli&rium Creplini and Jeannotii, Norman d (1854), Coup d'ceil Cycl. p. 2. 



Sal. Throughout Europe. Siberia. Kamtchatka. North Africa. Eng- 

 land and Ireland. (In lakes, canals, ponds, etc.) 



Cyclas lacustris is distinguished from the rest of the Cyclads by 

 the square or rather rhombic form of the shell, arising from its 

 thinly compressed expansion at the sides. It is also characterized 

 more than any other species of the genus by a cup-like capping of 

 the umboes, which is the embedded shell of the young fry. In 

 colour it is a semitransparent ash-tinged horn, smooth, but marked 

 at intervals, commonly rather distant, with lines of growth. The 

 animal is greyish- white, sometimes tinged with rose. 



