PLATE 101. 



Page 



Fig. 1. Eatonia pcmila. 437 



1. The cast of the ventral valve, natural size. 



Fig. 2 a - g. Eatonia peculiaris. 436 



2 a, b, c. Dorsal, ventral, and profile views of a specimen, having the ordinary form and 

 proportions of this species in the Oriskanj- sandstone. 



2 d. A cast of the dorsal valve of this species, showing the median septum and lateral 



lamella!. 

 2 e. A cast of the ventral valve, showing the form of the muscular impression, the median 



septum, and the small points of attachment for the adductor muscles. 



2/. A specimen preserving a portion of the shell, which, on one side, is penetrated by the 

 ramifying vessels. ( The lamellose structure of the shell is confounded with the surface 

 stri* in the figure, which gives it an unnatural appearance.) Figure enlarged to one and 

 a half diameters. 



2 g. A cast of the ventral valve, showing the muscular and vascular impressions ( See cor- 

 rected figure on Plate ci a). 



Fig. 3 a - m. Mebista lata. 431 



B a. Ventral valve of a young specimen. 

 3 6. Donsal view of a large specimen. 



8 c, d, e. Profile, ventral, and front views of the same specimen. 

 iif. A ventral view of an intermediate form. 



3 g. h. Dorsal and ventral views of a cast of this species. ( The mark of the median septum 

 is not shown in some of the figures.) 



3 i. Profile view of the same. 



8 k. Ventral view of an imperfect cast, showing a larger muscular area. 



8 I. Ventral view of a large individnal of this species. 



8 r«. Profile view of the sam^. 



