PLATE 1—Continued. 
Page. 
Fig. 14. Discina lodensis. 22 
14 a, b, c, e. Varieties of form of the dorsal valve. 
14 d,f. Ventral valves of the same species. 
Fig. 15. Discina truncata. 23 
15 a. A dorsal valve of the natural size. 
15 b. The same enlarged. 
Fig. 16. Discina minttta. 16 
16 a. A dorsal valve of the natural size. 
16 6. The same enlarged. 
Fig. 17. Discina alleghania. 25 
. 17 a. The dorsal valve of a large individual. 
17 6. A profile view of fig. 17 a. 
17 c'. The central valve of the same species. 
Fig. 18. Discina grandis.. 17 
18 a. A dorsal valve which is somewhat distorted. 
18 6. The interior of a ventral valve of the same species. 
