The Rogers Gap Fauna of Central Kentucky 



145 



2 — The eyes have a more anterior position. 



3 — The glabella descends more abruptly anteriorly into the 

 intramarginal groove. 



4 — The intramarginal groove is of greater depth and width, 

 and, consequently, the marginal rim is of a more pronounced 

 character. 



5 — The pygidium is more rounded and less triangular in out- 

 line. 



6 — The convexity of the pygidium is more uniform, there 

 being scarcely a suggestion of a flattened border. 



7 — The species is inferior in size, most of the specimens being 

 under 3^2 inches in length and none probably exceeding 4^ inches. 



8 — The cranidium is elongate as in Isoteliis gigas, but is not 

 quite as long or as triangular. (Fig. 3.) 



benicxmini 



r.benjamini Uotelus covinqtonensis ^-3^3^^ 



Isotelus coz'ingtonensis, Ulrich. Compared with Isoteliis hen- 

 jamini — 



1 — The outline of the cranidium in the antero-lateral part is 

 subangular, and, consequently, the preocular part is shorter (Fig. 

 2). The corresponding part of the outline of /. henjamini is more 

 regularly curved, and the cranidium is longer. 



2 — The angle formed by the converging edges of the post- 

 lateral extensions of the cranidium, between the facial suture and 

 the posterior margin of the cranidium, is smaller (Fig. 1). In /. 

 henjamini this angle is wider (Fig. 4). 



41 



