230 



NORTH AMERICAN INDEX FOSSILS. 



interstitial addition. Length about ^ to ^ inch, width slightly- 

 greater. 



Hamilton of New York, Ohio, Kentucky and Nevada. 



b e 



Fig. 280. a, Schuchertella arciostriata ; b, enlargement of surface; c* S c hucher- 



tella perversa. (After Hall. ) 



1 10. S. perversa (Hall). (Fig. 280, c.) Devonic. 



Subelliptical. Hinge line less than the greatest width of shell. 

 Length and width about as two to three. Front broadly rounded. 

 Pedicle valve very convex at umbo and less so toward the front • 

 beak distorted ; deltidium prominent and convex. Brachial valve 

 most convex above the middle, depressed toward the front. Sur- 

 face marked with distant, elevated striae, increasing by interstitial 

 additions ; interspaces crossed by elevated, undulating striae. 



Onondaga and Hamilton of New York, Nevada and Ontario. 



in. S. chemungensis (Conrad). (Fig. 281, a-b.) Devonic. 



Fig. 281. a, b, Schuchertella chemungensis (X %) 5 c ~ e , S. crenistria (X %) r 

 f, Orthotetes keok.uk. Cardinal regions of both valves viewed from within ; /, cardinal 

 process; s, median septum in pedicle valve; d, dental lamellae; I, teeth (X %)• 

 (After Hall.) 



Pedicle valve slightly concave, with prominent umbo. Angles 

 of the hinge line with the sides nearly rectangular. 



Chemung of New York, Pennsylvania, Ohio, Nevada, Manitoba. 



