cyclad^;. 279 



ner, like the Linnicei and other Gasteropodes, they 

 contrive to traverse the vessel from side to side, as 

 though they were crawling along a solid plane. 



This family contains two genera : — 



\.Cyclas. Shell oblong, subequilateral ; animal si- 

 phons two. (f. 1 — 3.) 



2. Pisidium. Shell ovate, inequilateral, wedge- 

 shaped; animal siphon one. (f. 4, 5.) 



1. Cyclas Lamk. (Cycle.) 

 Animal — mantle produced behind into two elongate 

 contractile siphons; foot tongue-shaped, very ex- 

 tensile ; shell suborbicular, nearly equilateral ; hind 

 teeth minute, one in the right and two in the left 

 valve; lateral teeth compressed, elongate, lamellar. 



The shells are known from the next genus by their 



being rounder and more equilateral. 

 112. 1. Cyclas rivicola. River Cycle, (t. 1. f. 1.) Shell 

 subglobose-ovate, ventricose, rather solid, beauti- 

 fully and closely striated, greenish brown, with 

 two or three darker bands ; edge and lunule yel- 

 low; umbones obtuse; cardinal ligament conspi- 

 cuous. 

 Tellina cornea /3. Maton 8c Racket, Linn. Trans. 

 viii. 59.; Turton, Conch. Diet. 180.; Wood, t. 

 46. f. 3. 

 Cardium corneum, var. Montagu, T. B. 86. 

 Cyclas cornea. Drap. Hist. Moll. 128. t. 10. f. 



1. 3. 

 Cyclas rivicola. Leach, MSS. ; Lam. Hist. v. 

 558. ; Pfeiffer, L. 8f TV. 121. t. 5. f. 3. 5. : Tur- 

 ton, Bivalves, 248. t. 11. f. 13.; Fleming, Brit. 

 Anim. 452. ; Jenyns, Trans. Camb. P. S. 6. ; Tver- 

 ton, Man. ed. 1. 12. f. 1. 



