Cyclas. mollusc a. CYCLADiE. 453 



behind, with prominent edges for the cartilage, which is dis- 

 tinct. 



Pectunculus subviridis, List. Conch, t. clix. f. 14 — Cvclas cornea, Drap. 



Moll. 128. t. X. f. 1, 2, 3. — Cyclas rivicola, Lam. Hist. v. 558. — Turt. 



Biv. Brit. 248, t. xi. f.;13 — Slow running streams, England. 

 Length y%ths, breadth ^'gthsof an inch ; cuticle yellowish or olive; often 

 darker, with pale bands ; less tumid, and more regularly curved in the out- 

 line than the preceding, of which it was supposed to be only a large variety 

 by Lister who had it from Doncaster, LinnaBUs from Iceland, and Montagu 

 from the Thames. The transverse grooves and coloured bands of both spe- 

 cies, depending on circumstances accelerating or retarding the growth of the 

 animal, furnish characters of uncertain value, though generally employed by 

 modern authors. 



54i6. C. lacustris. — Subinequilateral, with minute concentric 

 striae ; beaks prominent, with the margin in front thin and ele- 

 vated. 



Tellina lacustris, Mull. Hist. Verm. ii. 204. — Cardium lac. Mont. Test. 



Brit. 89 Cyclas lac. Drap. Moll. 130, t. x. f. 6. 7 — Turt. Biv. Brit. 



249, t. xi. f. 18.— Inflow running streams, England. 

 Length j\ths, breadth y^ths of an inch ; thin, glossy, transversely sub- 

 rhomboidal ; margin thin. 



547. C. amnicus. — Inequilateral, transversely ovate, and sul- 

 cated concentrically. 



Tellina amnica, Mull. Hist. Verm. ii. 205 — T. rivalis, Maton, Linn. 

 Trans, iii. 44, t. xiii. f. 37, 38. — Cardium amnicum, Mont. Test. Brit. 



86 Cyclas palustris, Drap. MoU. 131, t. x. f. 17, 18 — C. amnica, 



Turt. Biv. Brit. 250, t. xi. f. 15. — In slow runnijig streams. 

 Length about three-eighths, breadth half an inch ; greenish ; slightly pro- 

 duced anteally ; the margin in front of the beaks prominent ; the furrows of 

 the sulci are finely striated. 



EXTINCT SPECIES. 



1. C. deperditus Ovato-transverse, rather gibbous, umbonate ; lines of 



growth elevated, irregular ; central hinge teeth three, lateral ones two. — 

 Sower. Min. Conch, t. clxii. f. 1. — Plastic Clay. 



2. C. cuneiformis Transversely cuneate-ovate, gibbous ; lines of growth 



numerous, fine ; central hinge teeth three ; lateral ones two. — C. deperdita. 

 Park. Org. Rem. 111. 189, t. xiii. f. 5. — C. cun. Sower. Min. Conch, t. clxii. 

 f. 2, 3. — Plastic Clay. 



3. C. ohovatus Obovate, gibbous, anterior side obtuse ; beaks large ; cen- 

 tral hinge teeth three ; lateral ones two. — Sower. Min. Conch, t. clxii. f. 4, 5, 

 ^.-.-Plastic Clay. 



4. C. medius Transversely obovate, depressed, thick, smooth, anterior (?) 



side small, posterior rather pointed ; one tooth near the beaks in each valve. 

 — Cyrena media, Fitton, Annals of Phil. Nov. 1 824, 376. Cyclas medius. 

 Sower. Min. Conch, t. Dxxvii. f. 2.— /ra the fresh water Formation between the 

 Green and Iron Sand. 



5. C. membranaceus — Transversely obovate, depressed, smooth, very thin ; 

 anterior side small, posterior rather pointed. — Cyrena memb. Fitton^ Annals 

 of Phil. Nov. 1824, 376. Cyclas memb. Soiver. Min. Conch, t. Bxxvii. f. 3. 

 —•Weald Clay under Green Sand. 



