PLATE 10. 
Page 
Fig. 1 - 22. Ortii is or lata. 1*>- 
1.2.3. Individuals showing a gradation of size, from the smallest recognized specimens of 
the species to the half-grown forms. 
A. 5, 6. Individuals illustrating a mare elongate and more gibbous form, which seems scarcely 
separable from the others, but is still never found of larger size than fig. G. 
7, 8, 9. 10. Individuals of larger dimensions; the last being a full-grown specimen of the 
'broad variety, one and three-fourths inches wide by one and a quarter long. 
11, 12. 13, 11. The interior of the ventral valves of several specimens, showing some variety 
in the vascular impressions. 
15. 18. The interior of the dorsal valves of the more elongate and gibbous forms. 
17. The interior of the dorsal valve of the broad variety, having the dimensions of an inch and 
a half by an inch and a quarter. 
19, 20. Casts of the ventral valve, showing the muscular and vascular impressions. 
21. 22. Casts of the dorsal valve, with impressions of the cardinal and brachial processes. 
