58 
the ventral edge, slightly angular at the dorsal, narrower 
than the produced and dilated anterior side; anter.or 
dor: al edge nearly straight and angular at the end; dor- 
sal edge of the flat valve overlapping the concave one. 
0,45...0,80. Rare. 
P. Rostrata. Lam. 1.—Sow. G.—Sow. Sp. Con. f. 
7,8, 9.—E. M. t. 250.—TeErLina [NEQUIVALVIS. 
Lin. 1118.—D. p. 86.—Don. t. 41.f. 1.—Ch. f. 106. 
—P. MarearitTacea. Turt. B. p. 41. ¢.3. f. 11. fo 
(14.—P. Ivnequivatvis. ’. p. 466.—Oblong, ante- 
rior 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 
dnecurved. 0,70...1,40. Dawlish and Guernsey. 
TrIBE.—LITHOPHAGI: 
Borers, without accessory plates and more or less 
gaping anteriorly. Ligament external. 
Grenus.—HIATELLA. 
Transversely oblong, dorsal and ventral edges sub- 
parallel; hinge with the teeth obscure or with one 
tooth in one valve received into a cavity in the 
other. - 
H. Rvucosa, Flem. p. 461.-—Saxtcava. R. ana 
