316 T. E. SAVAGE ALEXANDRIAN ROCKS OP ILLINOIS AND WISCONSIN 



souri north of Saint Louis and northeastern Illinois, are well developed 

 and clearly exposed along Kankakee River about 5 miles south of Richey, 

 and hence these will hereafter be referred to by the name "Kankakee 

 limestone." From the similarity and abundance of the species of Strick- 

 landinia and other fossils in this horizon compared with those in the 

 upper part of the Gun River formation of the Anticosti region, it is 

 thought that this embayment in northeastern Illinois was connected 

 toward the northeast with the Anticosti Island region in the Gulf of 

 Saint Lawrence during Sexton Creek time. 



Description of Species 9 



genus schuchertella girty 



Schuchertella pecten var. robusta n. var. 



Plate 16, Figure 1 



Description: Shell semielliptical in outline; width about iy 2 times the 

 length; greatest width at the hinge line; cardinal extremities forming 

 nearly right angles with the sides, A nearly complete shell measures 

 l T /i6 inches long, iy 2 inches wide, and has a convexity of about 14 inch. 



Ventral valve moderately concave in general contour, but flattened 

 toward the cardinal extremities, the greatest concavity near the middle, 

 without mesial sinus ; beak moderately large, somewhat distorted ; cardinal 

 area of moderate height, extending to the extremities of the hinge line. 



Dorsal valve with convexity about equalling the concavity of the ventral 

 valve, highest near the middle, from which the surface curves rather 

 steeply to the cardinal margin and more gently to the front and lateral 

 margins; flattened toward the cardinal extremities; no mesial fold or 

 sinus ; beak inconspicuous. 



Surface of both valves marked by rather fine, narrowly rounded, or 

 subangular radiating striae of unequal size, which divide two or three 

 times between the beak and the margins, and by numerous very fine con- 

 centric lines, and a few much stronger lines of growth. 



Remarks : This variety differs from the very variable species S. pecten 

 of the Anticosti region in the larger size and coarser expression, the 

 greater convexity of the ventral valve, and the greater irregularity in the 

 size of the radiating stria?. 



Horizon and locality: Kankakee limestone, near Oswego, Illinois. 



9 The writer wishes to acknowledge his indebtedness to Prof. Charles Schuchert and 

 Dr. W. H. Twenhofel, through whose kindness a comparison of the species of fossils dis- 

 cussed and described in this paper was made with allied species of the Anticosti region. 



