276 



FRATERNUS. (N. sp.) 



Fig. 262. 



Fig. 263. 



Fig. 262. Illanus fraternus. a, part of the head ; 6, pygidium. 



263. /. consimiliK. a, part of the head ; b, pygidium ; c, side view of a; some of 

 the specimens are more abruptly arched. 



Description. Head very convex, forming about one-fourth of a sphere, 

 the posterior third distinctly tri-lobed by the dorsal furrows which are dis- 

 tant from each other about one-third the whole width. Eyes near the 

 posterior margin, and distant from the dorsal furrows about one-half the 

 width of the central lobe. Pygidium rather strongly convex, nearly semi- 

 circular, its length a little more than half the width at the front margin, 

 the posterior three-fourths of the margin uniformly rounded to the curve 

 of a semicircle very nearly, the anterior third obliquely truncated ; axis 

 one-third the whole length, not defined at the extremity. 



A specimen of the head without the fixed cheeks measures along the 

 curve on the median line, nine and a half lines ; width of the middle lobe, 

 four lines ; length of dorsal furrows, about three lines ; distance of the eye 

 from the dorsal furrow, two lines ; distance from the posterior angle of 

 the eye to the posterior margin, a little less than one line ; the length of the 

 eye is about one and a half lines. A detached cheek which occurs in the 

 same fragment of stone with several imperfect heads has the outer angle 

 well rounded and distant two and a half lines from the eye. In the pyg- 



