PLATE XXI. 
Leptodesma Rogersi. 
Page 176; 
Fig-. 1. A small block showing 1 two right valves of this species, X 2. 
Fig. 2. A large right valve preserving the mucronate extension of the wing, X 2. 
Figs. 3-8. A series of left valves varying in size and general proportion. Fig. 7 also shows a right valve. 
Fig. 9. A right valve of somewhat higher form than usual. 
Hamilton gi*oup. Norwich, Chenango Co., N. Y. 
Leptodesma spinigerum. 
Page 177. 
See Plate 89. 
Figs. 10-13. Four left valves showing slight variations of form and length of spine. 
Chemung group. Painted Post,'Steuben Co., N. Y. 
Leptodesma longispinum. 
Page 179. 
See Plate 89. 
Fig. 14. A left valve. This specimen is the original of fig. 3, p. 262, Geol. Rept. Fourth Dist. N. Y. 
Figs. 17-19. Three right valves. 
Chemung group. Painted Post, N. Y. 
Leptodesma robustum. 
Page 181. 
[^See Plate 89. 
Figs. 15, 16. Two left valves showing the form and convexity of the shell. The striae on the post-umbonal slope 
shoidd extend farther along this slope than represented, before recurving into the wing. 
Fig. 20. A rightlvalve. 
Chemung group. Painted Post, N. Y. 
