PLATE 13. 



Fig. 4 - 12. Orthis perelegans. 171 



4 a, b, c, etc. Views of small individuals, which appear to bo the young of tiiis species, but 



may prove distinct. 



5 a, b, c. Small individuals, authentic forms of this species, 

 ti a, b, c. Specimens intermediate in size. 



7 a, b, c, d & e. Specimens of the ordinary size. 

 8. A large individual of this species. 

 [) a, b. Interiors of the ventral valve. 

 10 a, b, c. Interiors of the dorsal valve. 



10 d. Profile showing the comparative elevation of the cardinal and brachial processes. 



11 a, b. c. Casts of the ventral valve. 



12 o, b. Casts of the dorsal valve. 



Fig. 16. Orthis peduncularis. 174 



16 a. Exterior of an imperfect valve. 

 16 b. Interior of the same. 



It is possible that this one may prove identical witli 0. cminens. 



