306 Review of the New York Geological Reports. 



has been assigned. The figure of this fossil given in Hall's Re- 

 port, differs but little from the figure of the /S. sericea 1 (p. 366, 

 Vol. xLviT,) of the Trenton limestone; it is said however to 

 have strongly marked elevated lines, with four to six fine striae 

 between each, which the /S*. sericea has not. These are, how- 

 ever, not distinctly shown in the figure. According to Hall, it 

 bears also a considerable resemblance to /S*. transversalis, a Wen- 

 lock shale fossil. If so, it must be much more convex in one 

 valve and more concave in the other, than the S. sericea. 



The Atrypa ajinis, figured below, is abundant in the upper 

 and lower green shale. This is the lowest position of this fossil. 



a 



The forms shown in Plate 18, are found in the Wolcott ore 

 bed, and are important, as they may serve as guides in tracing 

 out the ferruginous band. 



