the ventral edge, slightly angular at the dorsal, narrower 

 tha. the produced and dilaU'd anterior side; anterior 

 d<T al edge nearly straight and angular at ihe end ; djr- 

 sal edge of the flat valve overlapping the concave one. 

 0,45... 0,80. Rare. 



P. ROSTRATA. Lam. I. Sow. G. Sow. Sp. Con.f. 

 7, 8, 9.E. M. t. 250.TEJ LINA INEQUIVALVIS. 

 Lin. 1118. D.p. 86. Don. t. 41./ l.Ch.f. 106. 

 P. MARGARITACEA. Turt. B.p.ll. .3. /. 11. to 

 14. P. INEQUIVALVIS. F. p. 466. Oblong, ante- 

 rior side elongated, with two very ohtuse keels near the 

 dorsal edge, somewhat beaked and slightly truncated : 

 tooth in the flat valve small and blunt : hinge margin 

 incurved. 0,70... 1,40. Dawlish and Guernsey. 



TRIBE. L1THOPHAGI: 



Borers, without accessory plates and more or less 

 gaping anteriorly. Ligament external 



GENUS. H1ATELLA. 



Transversely oblong, dorsal and ventral edges sub- 

 parallel; hinge with the teeth obscure or with one 

 tooth in one valve received Jinto a cavity in the 

 other. 

 H. RTTGOSA. Flem. p. 461. SAXICAVA, R. and 



