238 



BRITISH MOLLUSKS. 



2. Cyclas cornea. Horny Cyclas. 



Shell; suborbital ar, thin, more or less globosely ventricose, very 

 finely concentrically striated, almost smooth, 

 bluish white, covered with a rather dull yel- 

 lowish horny or olive epidermis, inequilateral, 

 anterior side short, rounded, posterior ob- 

 liquely rotundately produced ; umboes obtuse, 

 ligament scarcely apparent. 



Musculus exiguus, Lister (1678), Hist. Anim. Angl. p. 150. 

 pi. ii. f. 31. 



Tellina cornea, Linnteus (1758), Syst. Nat. ed. 10. p. 678. 



Tellina rivalis, Miiller (1774), Verm. Hist, part ii. p. 202. 



Sphcerium corneum, Scopoli (1777), Intr. Nat. Hist. p. 

 397. no. 88. 



Cardium nux, Da Costa (1778) Test. Brit. p. 173. pi. xiii. 

 f. 2. 



Nux nigella, Humphreys (1797), Cat. Mus. Calonn. p. 59. no. 1088. 



Cyclas cornea pars, Draparnaud (1801), Tabl. Moll. p. 105. 



Cardium corneum, Montagu (1803), Test. Brit. p. 86. no. 14. 



Cyclas rivalis, Draparnaud (1805), Hist. Moll. p. 129. pi. x. f. 4, 5. 



Cyclas nucleus, Studer (1820), Kurz. Vers. p. 93. 



Tellina stagnicola, Sheppard (1823), Trans. Linn. Soc. vol. xiv. p. 150. 



Cyclas plumbeus, Villa (1841), Disp. Syst. Conch, p. 44. 



Cyclas flavescens, Macgillivray (1843), Hist. Moll. Aherd. p. 246. 



Cyclas Scaldiana, Normand (1844), Not. Nouv. Cycl. p. 5. f. 1, 2. 



Cyclas citrina, Brown (1845), Illus. Conch, p. 132. pi. xxxix. f. 37. 



Sphcerium citrinum and Scaldianum, Normand (1854), Coup d'ceil Cycl. 

 p. 1. 



Hah. Throughout Europe. Siberia. (Both in flowing and stagnant water.) 



This well-known species abounds in rivers, brooks, lakes, ponds, 

 ditches, and even in drains throughout Europe, from Lapland to 

 the islands of the Mediterranean, and over a large portion of Rus- 

 sian Asia. It is also closely represented in the United States by 

 Mr. Say's C. partumeia. Compared with C. rivicola, the shell is 

 very much smaller and more globose, but it is extremely variable. 

 Sometimes additions are made to the margin of the valves, gene- 

 rally of a paler colour than the rest, throwing the valves into a 

 convexity, which makes the shell almost as broad as it is long, 

 while sometimes, as in the specimen represented in our animal- 

 vignette, the valves are compressed with the umboes almost beaked. 

 The concentric sculpture of the shell is generally fine, sometimes 

 almost obsolete ; the epidermis is mostly rather dull. 



