332 EIGHTEENTH REPORT ON THE STATE CABINET. 



I received several years since a specimen of this species from Prof. C. 

 U. Shepard, who collected it with other Niagara fossils in Illinois, but 

 the record of the particular locality had been lost. 



Formation and locality. In the limestone of the Niagara group at 

 Waukesha and Milwaukee, Wisconsin, and from a similar horizon in Illinois. 



ILLiENUS IMPERATOR. 



IllcBnus imperater : Hall, Annual Report of Progress Geol. Survey of Wisconsin, 



1860, 1861. 



This species, which was described from some large caudal shields with a 

 few of the articulations of the thorax, has proved to be not rare. 



The head is large and broad, moderately convex, and pretty regularly 

 arching from the base to front; the glabella occupies about one-third the 

 entire width : dorsal furrows wide, extending about half the entire length 

 of the head, and curving outwards at the anterior extremity. 



One large head has a length of three inches and a half, with a width be- 

 tween the facial sutures of four and a quarter inches. The eyes and cheeks 

 are but partially known. 



The caudal shields present gradations in size, from a length of half an 

 inch by a width of seven-eighths of an inch, to those of less than three 

 inches long with a width of four and a half inches. The proportions of 

 length and breadth of the pygidium are not constant, though its wide and 

 very depressed form is always characteristic. 



The position of this species is somewhat lower in the group than the 

 Racine and Waukesha beds. 



ILL^NUS (BUMASTUS) BARRIENSIS. 



Bumastus barriensis : Murchison, Sil. System. 

 Bumastus barriensis : Pal. N. T., Yol. ii, pa. 302, pi. 66. 



This species is of common occurrence in the Niagara group of Wis- 

 consin, at Racine, Waukesha, Wauwatosa, and other places. 



It usually occurs as separated heads and pygidia, with detached portions 

 of the thorax. It has sometimes attained a very large size, the head being 

 two and a half inches in length ; equalling in size the largest head figured 

 from the Niagara shale of New-York. 



GENUS BRONTEUS (Goldfuss). 



BRONTEUS ACAMAS (n. s.). 



A cast of the head is broad : depressed convex, the anterior portion 

 plain ; dorsal furrow extending a little more than one -third the entire 

 length, A single glabellar furrow, with a distinct anterior lobe, are visible. 



The palpebral lobe is comparatively broad and moderately elevated. 



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