j 



PLATE 32 B. 



Fig. 1. 169. 16. Orthis occidbntalis. (Pag- 127.) 



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



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

 ly marked by the external radii. 

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



1 h, i. Interior of ventral valves, showing the medial tooth iuid the marks of the external radii. 



Fig. 2. 170. 17. Orthis srauATA, (Pag. 128.) 



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



2/, g, h. Profile views of specimens of different 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 t, k. Front views of young and old specimens. 



