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, f • -l^- 



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 ..I -^^^.—- Ceylon. 



P. Radiata. Sow. Spec. Con. t. 2./ 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. '^^^^.—W.Coluvibia. 



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

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

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

 ginated. — New Zealand. 



TRIBE LITHOPHAGI. 



Shells which bore into clay and other .mhstances, without accessory 

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

 ligament external. 



SAXICAVA. 



Inequilateral, obty.se, and transverse ; the anterior and ventral 

 margin gaping ; hinge nearly without teeth ; ligament external. 



S. RuGOSA.* Lam. 1, — Soiv. 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, g • • f • — N. Europe.^ 



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

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

 (;>flr^.)— Byssomya P. ? Bl. t. 80. bis. f. 5. — Li.st. t. 426./. 267. 

 Oblong, anteriorly more or less truncated, (sometimes produced 

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

 subterminal, ventral edge nearly straight and not incurved ; dirty 

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



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

 Pholadis is justly separated. 



