TRIBE CORBULACEA. 49 



106. — W. t. 5.f. 97. Oblong, anterior side elongated, with two 

 very obtuse keels near the dorsal edge, somewhat beaked and slightly 

 truncated : tooth in the flat valve small and blunt ; hinge margin 

 slightly arched, recurved. -J^.. 1|. — Europe. 



P. Oblonga. Soiv. Sp. Con. f. 10. Longer than Rostrata, 

 thin: anterior side rather beaked, with two very obtuse keels and 

 the hinge margin nearly straight ; ligament and tooth of the fiat 

 valve very small, -^j^. . l^^g. — Gamheroon. 



P. Depressa, Sow. Sp. Con.f. 11, 2. Ovate, more depressed 

 than the other species ; anterior side dilated ; valves nearly equally 

 fiat, two distinct teeth in the flatter, and one very large in the deeper : 

 dorsal edge somewhat arched, slightly recurved. ^.. ly^.' — Pacific. 

 P. Glacialis. Leach, iyi Ross. voy. — Sow. Sp. Con.f. A, 5, 

 6. Nearly oval, dorsal edge nearly straight; posterior side rather 

 produced, obtusely angular ; beak nearer the centre than in Obtusa : 

 tooth in the flat valve very small, f. — North Seas. 



P. Flexuosa. Sow. G. — Son. Sp. Con.f. 1,3, 4, 5. Oblong, 

 rather moi'e gibbose than in general ; anterior side elongated, sub- 

 rostrated ; ventral edge flexuous ; dorsal bicarinated, rather arched 

 and recurved: a rather short tooth, and an elongated, internal sub- 

 marginal plate on the anterior side of the flatter valve. -lo-xV- — 

 Red Sea. 



P. Unguiculus. Sow. Sp. Con. f. 16, 7. Oblong, i-ather 

 depressed ; anterior side narrower, rather produced, dorsal edge 

 nearly straight with two obtuse keels from the umbo to the end of 

 the beak : posterior side rounded or sub-truncated. 3__j>. 



P. Trilineata. Say. in Jo^irn. A. N. S. Phil. 2. — Conrad. 

 Am. C. t. 11./. i.--P. Nasuta. Sow. Sp. Con.f. 18, 9. Rather 

 lengthened, deeper valve with a flexuous margin : anterior side of 

 both valves beaked, their dorsal edge arched, I'ecurved : posterior 

 dorsal edge with a small projecting wing-like appendage : a distinct 

 tooth and an internal elongated sub-marginal plate in the anterior 

 side of the flatter valve ; two obtuse ratuer obsolete ridges in both 

 valves from the umbones along the anterior dorsal edge, -f^.. \-^^. — 

 N. America. 



P. Brevifrons. Sow. Spec. Con. t. 2. f. 25, 6. Elongated, 

 very thin, white and hyaline ; posterior side the shorter, rounded 

 and sub-angulated dorsally : anterior side the longer, beaked and 

 sub-truncated ; dorsal edge straight, ventral rounded ; a solitary 

 and very small tooth in the flattened valve. ^20^* — Panama. 



P. Arcuata. Sow. Spec. Con. t. 2.f 27, 8. Ovate, thickish, 

 opaque, pearly ; posterior side the shorter, rounded, anterior beaked; 

 dorsal edge arcuated, ventral rounded : an obsolete impressed groove 

 running from the umbo to the ventral margin, f • . 1 . — W. Columbia. 

 P. DiscoRS. Sow. Spec. Con. t. 2.f. 29, 30. Elliptic, depressed, 

 whitish, opaque : posterior side the shorter, anterior broader : 



