PLATE XXXTT. 

 Mytilakca u.mp.onata. 



I'age 257. 

 Figs. 1—1. The right, left, .•inti'i-inr iiml posterior views of an iinliviilual preserving both valves. The 

 si)ecimen has been slightly compressed laterally, giving an unnatural sharpness to the rostral 

 portions. 



Chemung group. Ithaca. iV. Y. 

 Figs. 5, 6. 7. The posterior, anterior and right sides of a specimen. Fig. G shows what appears to be the 

 pallial line tenninating near the beak. 



Chemung group. Mansfield, Pa. 



Mttilakca Ciiemungensis. 



P.lftC -258. 



Fig. 8. A small right valve showing the striated ligamental area. 



Chemung gi'Oup. Philipsburg, Alleghany Co., N. T. 

 Fig. 9. A left valve with the beak partially broken away showing the small cardinal teeth. 



Chemung group. Itockville, Alleghany Co., iV. Y. 

 Fig. 10. Tlie interior of a left valve from an impression in the shale, showing the striated hinge-area. 



Chemung group. Jiockvillc, i\r. Y. 

 Fig. 11. A small, broad right valve. 



Fig. 13. An impression of the margin of a large left valve, showing the form of the hinge and its breadth as 

 extending within the margin of the shell. 



Chemung gi-oup. Rockeille, N. Y. 

 Fig. 14. A very narrow and erect left valve showing also the striatioiis of the hinge. 



Chemung gi-oup. Ea.'^t Randolph, JV. I'. 



MviILARCA REOULARIS. 

 Page 260. 

 Fig. 12. A left valve showing the broad rounded form and straight erect beak. 

 Chemung group. Leim Ctnlre, Cattara^igus Co., N. Y. 



Mytilarca carinata. 



I'agc 2.")9. 

 See Plate 33. 

 Fig. 15. A small left valve. 



Chemung group. Near Elmira, N. Y. 

 Fig. 10. A small right valve showing the form of the shell. 



Chemung group. FactoryviUe, Tioga Co., N. Y. 

 Figs. 17, 18. Two opposite valves showing some variation in the form of the shell. 



Chemung group. Near Elmira, N. 1'. 

 Fig. 19. An internal cast preserving impressions of the cardinal and lateral teeth and showing the striated 

 ligamental area. 



Chemung group. Near Elmira, N. Y 



Mytilarca attexuata. » 



I'age 2('i0. 

 Fig. 20. A left valve showing the erect subcannate form and attenuate beak. 

 Chemung group. Elmira, N. Y. 



Byssopterta RADIATA. 



Page ~o'l. 



See Plate 80. 



Fig. 21. A right valve imperfect at the beak, but showing the surface characters and angular anterior .sitle. 



Fig. 22. An imperfect left valve which shows the general outline. The radii are not so distinctly dujilicate 



as on the other specimen. 



Chemung group. Mansfield, Tioga Co., Pa. 



