CTCLAS. 257 



b. Cardinal teeth single {rarely two divergent) ; shell 

 thin, suhquadrigonal ; umbones prominent. 



118. 5. Cyclas lacustris. Capped Cycle. — Shell 

 rather rhombic, compressed, thin, yellowish 

 white, diaphanous ; umbones prominent, 

 rather acute, and tuberculose ; ligament 

 inconspicuous, (t. 1. f. 3.) 



Cardium lacustre. Mont. T. B. 89. — Telllna lacustris. Linn. 

 Trans, vii. 60.; Turton, C. D. 180. — Cjclas calyculata. 

 Drop. 130. t. 10. f. 13, 14. ; Lam. Hist. v. 559. ; Pfeiffer, 

 122. t. 5. f, 17, 18.; Nilson, 99. ; Turton, Man. ed. 1. 14. 

 f. 3. ; Dupuy, Moll. Franc. 672. t. 24. f. 8. ; Forbes and 

 Lianley, B. M. ii. 118. t. 37. f. 7., t. O. f. 7.— Cyclas lacustris. 

 Turton, Biv. 249. t. 11. f. 18.; Leach, Syn. Moll. 289.— 

 Tellina tuberculata Alten, Syst. 4. t. 1. f. 1. — Cyclas tu- 

 berculata. Klees, 45. — Sphierium lacustre. Bourg. Splicer. 

 36. — Spbserium Brochoniaiium. Bourg. Sphar. 50. t. 3. f. 

 5. — Cyclas consobrina. Feruss. in Blainv. D. S. N. xii.. 

 279. — SphEeriuni Deshayesiauuui. Bourg. Anicen. 6. — Sphte- 

 rium ovale. Bourg. Sphcer. 31. t. 4. f. 6. 10. — Cyclas la- 

 custris. Forbes and Haidey., B. M. ii. 118. 



Young, the apex of the shell large relatively to the size of the 

 specimen. 



Inhab. rivers. 



Var. 1., shell orbicular, less compressed, subdiaphanous, red- 

 dish brown. 



Cyclas lacustris. Alder, Cat. i. 40., Brit. Mus. — Cyclas 

 calyculata )3. Jenyns, Monog. 11. 



Inhab. ponds. 



Var. 2., shell orbiciilar, rhombic, rather ventrlcose, subdiapha- 

 nous, reddish ; umbones less prominent, blackish. 



Cyclas stagnicola. Leach, MSS. fide Lam. — Cyclas caly- 

 culata, var. 2. Lam. Hist. v. 559. — Cyclas calyculata y. 

 Jenyns, Monog. 1 1 . 



Inhab. north of England. {Jenyns.) 



Animal white ; siphons white, elongate. 

 This species, when in confinement, shows more 

 activity than C. cornea ; they sometimes remain at 



s 



