TRIBE ARCACEA. 153 



heart -shaped, white spotted internally with brown. £. — New 

 Holland. 



A. Cardissa. Lam. 8.— Del. t. 11. f. 14. Nut-shaped and 

 transversely heart-shaped, valves keeled on the back, beaks almost 

 obsolete so as to cause the dorsal edge to seem quite flat ; the 

 ligamental area lozenge-shaped and flat ; ventral margin convex 

 and gaping. J-, — British Channel. — A small inequilateral shell 

 of an extraordinary shape for this genus. Placed on the pointed 

 extremity of its elongated side, it wears the semblance of Cardium 

 Cardissa, but without any apparent beaks. 1 



A. Sulcata. Lam. 11. Ovate, very obtuse posteriorly, and 

 obliquely truncated anteriorly, entire, gaping ; white clouded with 

 reddish brown, with longitudinal grooves which are transversely 

 striated and subcrenated. 1^. — New Holland. 



A. Ovata. Gmel. 3307.— Lam, 12.— W. t. 9. /. 12— A. 

 Nivea. D. p. 230.— Ch. f. 538.— E. t. 309. /. 3. Ovate, 

 somewhat sinuated, ventricose, but depressed in the middle and 

 rather angulated at one end, with crowded narrow decussated ribs 

 under a scaly and brown epidermis, margin gaping in the middle, 

 no posterior depression. If ..2|. — Red Sea.— Deshayes holds 

 this to be the same as Helbingii. 2 



A. Barbata. Lin. 1140.— D. p. 229.— Lam. 13.— W. t. 9. 

 /. 3.— Ch.f. 535.— Bl. t. 65. f. l.—E. t. 309. /. 1. Trans- 

 versely oblong, depressed, somewhat sinuated in the middle, 

 reddish brown becoming paler centrally under a brown epidermis 

 which forms shaggy bristles on the crowded raised longitudinal 

 striae, (crossed by delicate transverse ones) ; margin nearly closed, 

 the umbones depressed but the beaks not distant, and the area 

 between them covered by a brown ligament which adheres to it by 

 means of several grooves nearly parallel to the hinge. — Variety. 



1 A. Ventricosa. Lam. 9. being but a variety of No^e must 

 be suppressed. — Deshayes. 



A. Retusa. Lam. 10. — Ch. f. 432. Oval, ventricose, obtuse 

 at each end, decussated by the striae, the longitudinal grooves sub- 

 imbricated : ligamental area brown and glabrous. — The specimens 

 in the French Museum, being old Navicular es and the figure of 

 Chemnitz being universally assigned to Imbricata, it is probable 

 that this species must be expunged from our future catalogues. 



2 Of this species, Deshayes considers as a variety the A. Tra- 

 pezina. Lam. \8.— Del.t. 11./. 13. Ovate, elongated, sub tra- 

 peziform, depressed, pellucid, longitudinally grooved and transversely 

 striated, the umbones smooth, the anterior edge very oblique and 

 incurved, ventral arcuated ; area between the beaks concave and 

 rather narrow. H. — Timor and South Seas. 



