PLATE XXI—Continued, 
Leptodesma potens. 
Page 188. 
‘ See Plates 22 and 89. 
Fig. 21. A right valve referred to this species. 
Chemung group. Conewango, Cattaraugus Co., N. Y. 
Fig. 30. A left valve showing the form and proportions of the shell. 
Chemung group. Portville, Cattaraugus Co., N. Y. 
Leptodesma protextum. 
Page 183. 
Figs. 22, 23. A left and a right valve in the same association. 
Chemung group. Chemung river, Upper Narrows, N. Y. 
Leptodesma sociale. 
Page 187. 
Figs. 24, 25. Two left valves showing the form of the shell and surface ornamentation, X 2, from fig. 27. 
Chemung group. Conewango, Cattaraugus Co., N. Y. 
Fig-. 26. An enlarged view of a right valve from the same block. 
Fig. 27. A fragment of stone with several valves of this species, natural size. 
Fig. 28. An impression of a left valve, retaining a part of the right valve in place. 
Chemung-group. Conewango, Cattaraugus Co., N. Y. 
Fig. 33. A fragment of rock with a right and a left valve showing their comparative form. 
Chemung group. Broome Co., N. Y. 
Fig. 34. A right valve of larger size and broader form, associated with fig. 33. The extremity of the wing 
should be produced farther than is represented. This and the preceding figure are referred 
to this species with some doubt. 
Leptodesma Moetoni. 
Page 190. 
See Plate 89. 
Figs. 29, 31. Two left valves varying somewhat in siz.e and proportions. 
Fig. 32. A right'valve. This specimen is redrawn on plate 89, fig. 10. 
Chemung group. Portville, Cattaraugus Co., N. Y. 
Leptodesma Lichas. 
Page 232. 
See Plate 91. * 
Figs. 35-37. Three left valves. 
Fig. 38. A large left valve of this species. The cardinal extremities should be produced in the figure to 
correspond with fig. 37. 
Fig. 39. A small right valve. 
Chemung group. Philipsburg, Alleghany Co., N. Y. 
Leptodesma lepidum. 
Page 195. 
See Plate 89. 
Fig. 40. A lpft valve, as seen lying in the rock, and with a part of the rig-ht valve in place. The concavity 
of the margin of the wing is represented as too deep. 
Chemung group. Philipsburg, N. Y. 
