50 TESTACEOUS MOLLUSCA. 



dorsal edge anteriorly sub-arcuated, posteriorly rounded, ventral 

 rounded, anteriorly ventricose ; left valve anteriorly with radiating 

 lines, a conspicuous keel near the anterior dorsal edge. ■§-. .-J-J. 



P. Ceylonica. Sow, Spec. Cone, t, 2.f 20, 1, 2. Elongated, 

 depressed, sub flexuous, anteriorly beaked, anterior dorsal edge 

 arcuated and recurved, posteriorly dilated ; two strong teeth and a 

 marginal lamina in the flat valve, a single arched one in the other. 

 f..l T V — Ceylon. 



P. Radiata. Sow. Spec. Con. t. 2.f. 23, 4. Ovate, rather 

 depressed, white with rufous linear rays on the flat valve ; anterior 

 side longer, sub-truncated and its dorsal edge straight, posterior 

 side small ; ventral margin rounded. 7 ^ 2 .~W. Columbia, 



P. Striata. Quoy. Ast. t. 83./. 10. Ovate-triangular, rather 

 solid, with transverse plait-like strise, depressed, posteriorly obtuse, 

 anteriorly sub-angulated ; sub-equilateral ; apex: acute and emar- 

 ginated. — New Zealand. 



TRIBE LITHOPHAGI. 



Shells which bore into clay and other substances, without accessory 

 valves or sheath, and more or less gaping at their anterior side ; 

 ligament external. 



SAXICAVA. 



Inequilateral^ obtuse, and transverse ; the anterior and ventral 

 margin gaping ; hinge nearly without teeth; ligament external. 



S. Rugosa.* Lam. 1. — Sow. G — Reeve, t.50. — Mytilus R. 

 Lin.?—D. p. 304. (part)-W. t. 12. /. 9. Ovate, obtuse at each 

 end, anterior side at least twice as long as the posterior, the ventral 

 edge incurved in the middle ; dirty white, strong, coarse, with 

 transverse wrinkles and the epidermis yellowish ; beaks not ter- 

 minal : if with two ridges on the anterior slope, the ridges very 

 obscure. \ . .-J . —N. Europe. 1 » 



S. Pholadis * Lam. 3. — Distorta. Say. — Gould Mas.f. 

 40.— Rugosa. Turt. Biv. t. 2.f. 10.— Mytilus. R. D. p. 304. 

 (part.)— Eyssomya P. ? Bl. t. 80. bis.f. 5. -List. t. 426./. 267. 

 Oblong, anteriorly more or less truncated, (sometimes produced 

 and attenuated, as often dilated,) posteriorly obtuse and the beaks 

 subtermmal, ventral edge nearly straight and not incurved ; dirty 

 white, strong, coarse, (the epidermis yellowish, ) with concentric 



1 S. Galltcana. Lam 2. is a var (fide Desh ) I doubt whether 

 Pholadis is justly separated. 



