PLATE XXI. 

 Leptodesma Rogersi. 



Page 176. 

 Fig. 1. A small block showing 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. A series of left valves varying in size ami general proportion. Fig. 7 also shows a right valve. 

 Fig. 9. A right valve of somewhat higher form than usual. 



Hamilton group. Norwich, Chenango Co., X. T. 



Leptode>ma rpesigerum. 



Page 177. 

 See Plate S9. 

 Figs. 10-13. Four left valves showing slight variations of form and length of spine. 

 Chemung group. Painted Past. Hfeubcn Co.. X. 1". 



Leptodesma longispintjm. 



Page 179. 

 See Plate S9. 

 Fig. 14. A left valve. This specimen is the original of fig. 3, p. 202, Geol. Rept. Fourth Dist. X. V. 

 Figs. 17-19. Three right valves. 



Chemung group. Painted Post, X. Y. 



LEFrODESllA KOBUSTUM. 



Page 1-1. 



:See Plate SO. 



Figs. 15, 16. Two left valves showing the form and convexity of the shell. The striae on the post-umbonal slope 



should extend farther along this slope than represented, before recurving into the wing. 

 Fig. 20. A rightvalve. 



Chemung group. Painted Post, N. T. 



