PLATE 12. 
Page 
168 
Fig. 1-6. Orthis planoconvexa. 
1 a, b. Views of small individuals of this species, from Maryland. 
2 a, b, c, d, & 3. Larger individuals, from New-York, showing the ventral and dorsal sides. 
profile and area. 
4. The interior of the dorsal valve of a smaller individual. 
5. Interior of the ventral valve. 
ti a, b. Dorsal and ventral valves of a cast of the same species. 
Fig. 7 - 21. Orthis subcarinata. 
7, 8 a , b, c. Views of young individuals. 
9, 10. Views of individuals which have a subquadrangular outline, with the dorsal valve 
deeply depressed in the centre and much elevated on each side, and the front margin 
strongly sinuate. 
11, 12. Interior of the valves of the preceding specimens. 
13. 14, 15. Individuals showing gradation in size, and some slight modification in proportions. 
16, 17. Full-grown individuals of this species. 
18. Interior of the ventral valve. 
19 a, b. Interior of the dorsal valve, showing the muscular and vascular impressions, and car¬ 
dinal view of the same. 
20. 21 a. b. c. Ventral, dorsal, and profile views of casts, the vascular impressions, etc. 
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