PLATE 10 A. 



Page 



Fig. 1, 2, 3. Okthis concinna. 172 



1 a, b. Ventral and dorsal views of a small specimen. 



2 a, b, c, d. Ventral, dorsal, profile, and front views of a large individual. 



3 a, b. Interiors of the ventral and dorsal valves. 

 3 c. Cardinal view of the dorsal valve. 



Fig. 4, 5 & 6. Orthis oblata, »ar. emaroinata. Iti4 



4 a, b, c, d. Illustrations of the form and characters of this variety. 



6 a, b. Interior of the two valves. 



6 a, 6. Cast of the ventral and dorsal valve. 



Fig. 7 - 12. Orthis discus. 16.5 



7; 8 o, ft. Individuals of the smaller known forms of this species. 

 9, 10 a, ft. Individuals of larger size. 

 10 c, d. Cardinal and front views of the same. 



11. Interior of the ventral valve. 



12. Cast of a doi-sal valve, probably of this species. 



Fig. 13 a, b. Orthis deformis. 174 



13 o. Dorsal view, showing the extent" of area, the broken beak, etc. 



13 ft. Ventral valve of the same, showing the abrupt contraction of the stria; towards the beak, 

 which is broken oflT below the point of attachment. 



Fig. 13, 14, 15, 16. Skenidium (Orthis) insignis. 173 



13. Dorsal view, natural size. 



14 & 15. Dorsal valve and area enlarged. 



16. Front view of the same enlarged. 



