TRIBE ARCACEA. 157 



* * Inner margin crenulated, 



A. Helbingii. Lam. 24. — A. Candida. Gmel. 3311. — D. 

 p. 228. — Ch.f. 542.— TV. t. O.f. 7. Transverse, anteriorly pro- 

 duced, posteriorly truncated, white under a scaly epidermis, with 

 longitudinal crenulated grooves, which are in pairs at the anterior 

 end : beaks approximated, margin gaping and somewhat crenu- 

 lated. 2. — Guinea and Brazil. — " Probably a variety of Ocata." 

 Desh. 



A. Scapha. Lam. 25. — Ch. f. 548. Transversely oblong, 

 ventricose, thin, white with the umbones reddish and oblique ; 

 with from twenty-nine to thirty-four ribs, which are divided into 

 two portions by a groove, (which is narrow but almost as deep as the 

 spaces between the ribs,) and are narrow and prominent parti- 

 cularly on the anterior side. 5 — India ? — TV. Indies ? 



A. Antiquata. Lin. 1141.— D. p. 232.— Lam. 26.— TV. t. 

 g.f \7.— Ch.f. 548.— E. t. 306./. 2.— Glial, t. 87. c Trans- 

 versely ovate, obliquely heart-shaped, thick, white, ventricose, with 

 numerous flattened ribs, which are transversely striated, unarmed 

 and the posterior ones bifid: anterior side slightly angulated: area 

 between the beaks not grooved. 2. . 3. — Mauritius, Mada- 

 gascar, S?c. x 



A. Rhombea. Born.— Gmel. 3314.— D. 233.— Lam. 27. — 

 Ch.f 553.— E. t.307 f3.—W. t. 9.f 19. Heart-shaped, nearly 

 as long as broad, gibbous, white covered by a brown epidermis, 

 with about twenty-six longitudinal transversely striated ribs, and 

 their interstices nearly smooth: beaks incurved and distant, the 

 area between them rhomboidal. 1^. . lj. — TV. Indies. — E. Indies? 



A. Granosa. Lin. 1142.— D. p. 233.— Lam. 28.— TV. t. 9. 

 f. 18.— List. t. 241. /. 7S.-CJi.f.557.—Xnorr.3.t.4.f.2.-~ 

 Sow. G. — Reeve, t. 82. f 3. Heart-shaped, nearly as iong as 

 broad, very ventricose, thick, almost equilateral, with upwards of 

 twenty rounded ribs, armed with orbicular, somewhat spinous 

 nodules, white within, and without, tinged slightly with brown at 

 the beaks, which are incurved and rather distant with the area 

 between them covered with a dark brown ligament, marked with 

 rhomboidal grooves. If. . 2. — Indian Ocean. 



A. Auriculata. Lam. 29.— Del. t. 11. f 12. — Savig. 

 Eyyp. t. 10. f 8. Heart-shaped, ventricose, white, under a hairy 

 epidermis, with about twenty-eight strong radiating crenulated 



1 Deshayes separates as confounded with this, a species which I 

 propose to name in honour of that laborious savant, A. Des~ 

 hayesii. — Gual. t. 87. B.—E. t. 306./. 1. Oblong, rather thin, 

 with rounded ribs and the area between the beaks marked with 

 lozenge-shaped grooves. 



