TO GEOLOGY. 77 



His valuable contributions to science are too well known 

 to need my observing upon them. 



P. minor. Plate 3. Fig. 54. 



Description. Shell angular above and round below, 

 nearly equilateral, with minute radiating ribs cut by 

 transverse striae ; beaks rather elevated ; hinge teeth 

 arched, large, diminishing only at the anterior and pos- 

 terior parts of the row ; cicatrices impressed ; cavity of 

 the shell shallow ; marginal teeth small and square. 



Diam.,2, Length .4, Breadth 9-20ths, of an inch. 



Observations. This diminutive species resembles in 

 some of its characters, the Broderipii, but differs from it 

 entirely in the dorsal line and the marginal teeth. 



P. deltoideus. Plate 3. Fig. 55. 



Description. Shell subtriangular, inequilateral, more 

 rounded before, acutely angular at the beak, with minute 

 longitudinal ribs cut by transverse striae ; beaks elevated, 

 pointed ; hinge teeth smaller in the centre ; cicatrices 

 impressed ; cavity of the shell shallow ; marginal teeth 

 rather large and square. 



Diam, 5-20ths, Length .4, Breadth .4, of an inch. 



Observations. Closely allied to the P. minor, this species 

 resembles it in nearly all its characters. It differs in out- 

 line, and more particularly in the angle of the dorsal mar- 





