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. =',..12.—Hurope. 
P. Ogptonea. Sow. 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 flat 
valve very small. %,..144,.—Gamberoon. 
P. Depressa. Sow. Sp. Con. f.11, 2. Ovate, more depressed 
than the other species ; anterior side dilated; valves nearly equally 
flat, two distinct teeth in the flatter, and one very large in the deeper : 
dorsal edge somewhat arched, slightly recurved. +..1;4.—Pacific. 
P. Guacratis. Leach. in Koss. voy.—Sow. Sp. Con. f. 4, 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. #.— North Seas. 
P. Furxvosa. Sow. G'.—Son. Sp. Con. f. 1,3, 4,5. Oblong, 
rather more 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. ;3,..45.— 
fed Sea. 
P. Uneuicutus. Sow. Sp. Con. f. 16, 7. Oblong, rather 
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,,°. 
P. Trirrneata. Say. in Journ, A. N.S. Phil. 2.—Conrad. 
Am. C.t.11.f. iP. Nasura. Sow. Sp. Con. f. 18, 9. Rather 
lengthened, deeper valve with a flexuous margin: anterior side of 
both valves beaked, their dorsal edge arched, recurved: 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 rather obsolete ridges in both 
valves from the umbones along the anterior dorsal edge. =%,..153;.— 
N. America. 
P. Brevirrons. 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. 7538.— 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. 2..1.—W. Columbia. 
P.Discors. Sow. Spec. Con. t. 2.7.29, 30. Elliptic, depressed, 
whitish, opaque: posterior side the shorter, anterior broader ; 
E 
