TRIBE MY A HI A. 25 



A. Ovalis. Stvtck. Z. J. 5. t. sup 43. f. 7, 8. Inequivalve, 

 tbiu, pellucid, posteriorly truncated : more convex valve sulcated at 

 the upper edge, and receiving the inflected edge of the other valve 

 which is slightly convex ; hinge with an oblique elongated internal 

 cartilage. 3 ^ 4 . 



A. Pandoriformis. Stutch. Z. J. 5. t. sup. 43. f. 3, 4. 

 Plano-convex, subovate, with transverse distant striae ; convex valve 

 posteriorly carinated and truncated, the other valve slightly concave; 

 hinge with a flat testaceous piece attached by the cartilage to the 

 cardinal pits ; an indistinct depressed line obliquely crossing the 

 internal disc of each valve, from the umbones to the ventral mar- 

 gin . W- 



A. Crassa. Stutch. Z. J. 5. p. 100. t. sup. 43. /. 5, 6. Thick, 

 subtriangular, inequivalve, transversely ribbed : one valve slightly 

 convex, posterior side of both valves carinated, with a smooth cordate 

 posterior depression. 5_ 6 . 



striae towards the ventral edge and anterior end, where the epidermis 

 is wrinkled ; beaks prominent, inside polished, tooth broad, erect, 

 little elevated, with its anterior edge fitting into the slight groove of 

 a projecting plate in the opposite valve. i«-f. — U. States. 



O. Elongata. Gray in Brit. Mas. — A Truncata. Lain, in 

 part. Nearly thrice as broad as long, very inequivalve, beaks situated 

 at -fths the distance from the rounded posterior extremity, ventral 

 and dorsal edges but little curved, subparallel in the centre ; ante- 

 riorly subrostrated but truncated at the extremity, the gape very 

 large ; very fragile, pellucid, the epidermis with fine radiating lines' 

 not visible on the disc. &. . 1 1. — Mediterranean. 



0. Brevifrons. — Lyonsia B. Sow. Z. P. 1834. Oblong, 

 palish, the epidermis obscure and horny : posteriorly short and 

 acuminated, anteriorly longer and attenuated ; dorsal edge anteriorly 

 elongated and straightish, posteriorly short and sloping, ventral edge 

 with a large elongated sloping gape at the posterior extremity. 2 -g- 4 . 

 — IT 7 '. Columbia. 



0. Picta. — Lyonsia P. Sow. Z. P. 1834. Obovate, anteriorly 

 rounded, thin, anteriorly broader ; the epidermis brown, painted 

 with wavy black lines : dorsal edge sloping posteriorly, anteriorly 

 straightish ; ventral edge with a small posterior gape, anteriorly 

 rounded. x \ -± 7 . — TI 7 ". Columbia. 



0. Cuneata. — Anatina C. Gray. Spic. Z. t. 3. f. 14. 

 Solid, irregular, subequivalve, oblong-wedgeshaped, anteriorly pro- 

 duced, posteriorly very short, subtruncated and rounded ; with 

 irregular concentric wrinkles, pearly within ; periostraca hard, 

 greenish, extending beyond the margin ; hinge almost toothless, 

 with a large moveable oblong tooth-like appendage. |..1J. — 

 Peru. 



