PLATE 10 A. 
Page 
172 
Fig. 1, 2, 3. Orthis concinna. 
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. 
8 a, b. Interiors of the vc-ntral and dorsal valves. 
3 c. Cardinal view of the dorsal valve. 
Fig. 4, 5 & 6. Orthis oblata, var. emarginata. 164 
4 a, b, c, d. Illustrations of the form and characters of this variety. 
5 a, b. Interior of the two valves. 
6 a, b. Cast of the ventral and dorsal valve. 
Fig. 7-12. Orthis discus. 165 
7. 8 a, b. Individuals of the smaller known forms of this species. 
9, 10 a, b. Individuals of larger size. 
10 c, d. Cardinal and front views of the same. 
11. Interior of the ventral valve. 
12. Cast of a dorsal valve, probably of this species. 
Fig. 13 a, b. Ortiiis deformis. 174 
13 a. Dorsal view, showing the extent of area, the broken beak, etc. 
13 b. Ventral valve of the same, showing the abrupt contraction of the striae towards the beak, 
which is broken off 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. 
