PLATE 2— Continued. 



Page 



Figs. 19-22. DisciNA DORiA 19 



19. Vertical view of a specimen of an upper valve ; enlarged two diameters. 



20. Profile of the same, from Canada West. 



21. A dorsal valve of the same species, natural size. 



22. A group of specimens attached to a univalve shell. 



Figs. 23, 24. DisciNA seneca . . . r 20 



23. Vertical view of a dorsal valve, natural size. 



24. Profile of the same. 



Figs. 25-28. DisciNA media 20 



26. 26. Dorsal and ventral valves, natural size. 



27. A ventral valve enlarged two diameters. 



28. A specimen of the ventral valve of this species, from the Chemung group. 



Fig. 29. DisciNA MEDIA var 21 



29. A ventral valve from the Marcellus shale. 



Figs. 30, 31. DisciNA doeia.? 21 



80. A vertical view of a dorsal valve, which Is rather more convex than usual in this species. 

 31. A profile of the same. 



Figs. 32, 33. DisciNA ORANDI6 17 



82. A profile showing the usual elevation. The line surrounding this figure gives the ele- ' 

 vation of a specimen referred to this species, Plate 1, flg. 18 a. 



33. A fVagment of rock with a group of four individuals of this species. 



Fig. 34. Disc INA RANDALLI , 18 



34. The lower side of a ventral valve, natural size. 



Fig. 86. DisciNA LODENSIS 22 



86' A group of three ventral valves, natural size. 



Figs. 86, 37. DisciNA truncata 23 



86, 87. Dorsal and ventral valves enlarged to three diameters. 



Figs. 38, 39. DisciNA ELMiRA 24 



88. A dorsal valve, vertical view. 



89. Profile of the same. 

 40. Undetermined. 



