TO GEOLOGY. A 
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 strie; 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 strie ; 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- 
