MOLLUSCA. CYCLADiE. 
Cyclas. 
■m 
behind, with prominent edges for the cartilage, which is dis- 
tinct. 
Pectunculus subviridis, List. Conch, t. clix. f. 14.— Cyclas cornea, Drop. 
Moll. 128. t. X. f. 1, 2, 3. — Cyclas rivicola, Lam. Hist. v. 558. — Turt. 
Biv. Brit. 248, t. xi. f.l3 — Slow running streams, England. 
Length x®oths, breadth x’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, Linnaeus 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. 
546, 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. Biv. Brit. 
249, t. xi. f. 18.— In slow 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. Moll. 131, t. x. f, 17, 18. — C. amnica, 
Turt. Biv. Brit. 250, t. xi. f. 15. — In slow running 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-trans verse, 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. Bern. 111. 189, t. xiii. f. 5 — C. cun. Sower. Min. Conch, t. clxii. 
f. 2, ^.—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. 1824, 376. Cyclas medius. 
Sower. Min. Conch, t. Dxxvii. f. 2.— the fresh water Formation between the 
Green and Iron Sand. 
5. C. memhranaceus — Transversely obovate, depressed, smooth, very thin ; 
anterior side small, posterior rather pointed.— Cyrena merab. Fitton.^ Annals 
of Phil. Nov. 1824, 376. Cyclas raemb. Soiver. Min. Conch, t. nxxvii. f. 3. 
•—Weald Clay under Green Sand. 
