PLATE 32 B. 



Fig. 1. 169. 16. Okthis occidentalis. (Pag. 127.) 



1 a, b. Cardinal views of a young and old specimen of this species. 



1 c. Ventral valve of an imperfect specimen, partially showing the interior of the dorsal valve, wliicli is strong- 

 ly marked by tlie external radii. 

 1 d. Profile view of a large specimen. 1 e,f, g. Views of ventral valves. 



1 /(, i. Interior of ventral valves, showing the medial tooth and the marlcs of the external radii. 



Fig. 2. 170. 17. Okthis siNCATA. (Pag. 128.) 



2 a, b, c, d, e. A series of specimens, illustrating the variations produced by age. 



2y, g, h. Profile views of specimens of difierent ages, showing the gradual increasing rotundity of the ventral 



valve, and also the more acute beak of the dorsal valve as compared to the last. 

 '2 i, /(. Front views of young and old specimens. 



