FOSSILS OF THE HUDSON RIVER GROUP. 103 



This species differs from B. oculifera in being destitute of the prom- 

 inent eye tubercle. 



Formation and locality : In the Hudson River rocks, at Cincinnati, Ohio. 



BeYRICHIA OCULIFERA. 



Plate 4, figs. 9, 10. 



Beyriclnn oculifera, Hall; Descr. New Species of Fossils from the Hudson River Group, 



etc., p. S. 

 Beyrichia oculifera, Hall; 24th Rept. State Cab., p. 232, pi. S, figs. 9, 10. 



Carapace small, seldom exceeding seven-hundredths of an inch in 

 length, by three to four-hundredths in the greatest breadth, in the 

 largest specimens ; valves obliquely sub-reniform, broadest near the an- 

 terior end, with a straight hinge line, which is a little shorter than the 

 greatest length of the valve; anterior end projecting beyond the hinge ; 

 center moderately convex, with a proportionally broad, deep channel, 

 just within the margin, extending all around it, except for a short dis- 

 tance at the posterior extremity, near the dorsal margin. The body of 

 the valve is crossed obliquely by two broad, deep furrows, having their 

 origin on the dorsal margin, the posterior one situated a little more than 

 one-third of the length of the valve from the jDOsterior extremity, and 

 extending full^y two-thirds across it; the anterior furrow is situated just 

 behind the anterior third of the length, and in its lower portion is more 

 strongly curved forward than the other. Eye tubercle large, peduncu- 

 lated, very prominent, and spreading at the top, its surface equal to 

 about one-third the width of the valve, and its height at the posterior 

 margin equal to the breadth at the top, while the anterior margin is but 

 little elevated, giving an obliquely sloping circular surface, with a den- 

 ticulated border. This surface, under a strong magnifier, is seen to be 

 covered b}^ fine, eye-like facets, similar to those of the eyes of trilobites of 

 the genus Illasnus. 



This species is very distinct from any other described, in the form and 

 strength of the transverse furrows, and especially in the great jDrom- 

 inence of the club-shaped eye tubercle. So far as can be ascertained, it is 

 the first species of this group of crustaceans in which the eye facets have 

 been detected. 



Formation and locality : In the shales of the Hudson River group, near Cincinnati 

 Ohio. 



