Figs. 1- 
Fig. 4. 
Fig. 5. 
Fig. 6. 
Fig- 7. 
'Fig. 8. 
Fig. 9. 
Fig. 10. 
Figs. 11, 
Fig. 13. 
Fig. 14. 
Figs. 15, 
Fig. 17. 
Fig. 18. 
PLATE XC. 
b — Umbonata. 
Leptodesma Medon. 
Page 197. 
-3. Three left valves varying somewhat in form and size. 
A right valve of this species. 
Chemung- group. Lawrenceville, Tioga Co., Pa. 
Leptodesma Mentor. 
Page 205. 
See Plate 23.. 
A left valve of the usual form. 
Chemung group. Smethport, Pa. 
Leptodesma Cadmus. 
Page 201. 
-A left valve of a specimen preserving both valves partly open. 
Chemung group. Smithfield, Bradford Co., Pa. 
A large left valve. 
Chemung group. Steuben Co., N. Y. 
Leptodesma Orodes. 
Page 206. 
See Plate 25. 
The specimen fig. 9, plate 25, redrawn to show the - true form of the body and wing. 
Chemung group. Smethport , Pa. 
Leptodesma umbonatum. 
Page 198. 
See Plate 22. 
The specimen fig. 13, plate 22, redrawn to show its proper form and proportions. 
Chemung group. Twenty Mile creek, Chautauqua Co., N. Y. 
Leptodesma umbonatum, var. depressum. 
Page 199. 
See Plate 22. 
The specimen fig. 14, plate 22, redrawn and restored in outline. 
Chemung group. Napoli Centre, Cattaraugus Co., N. Y. 
Leptodesma Creon. 
Page 202. 
12. Two left valves showing slight differences in form and surface markings. 
A right valve. 
Chemung group. Lavyrenceville, Tioga Co., Pa. 
Leptodesma Loxias. 
Page 201. 
A left valve of this species. 
Chemung group. Lavyrenceville, Tioga Co., Pa. 
Leptodesma Demus. 
Page 203. 
16. A right and left valve showing the usual form of the shell. 
Chemung group. Lawrenceville, Tioga Co., Pa. 
c — Rostrata. 
Leptodesma extenuatum. 
Page 207. 
See Plate 22. 
The specimen fig. 23, plate 22, redrawn to show the entire form and proportions. 
A right valve with the test removed showing the pallial line and muscular impression. 
Chemung group. Mansfield,, Tioga Co., Pa. 
