313 



thoi'Mx, width ecjiial to length: surface scarcely trihjbate 

 and axis ver^' broad : plenra^ narrow, deflected along their 

 median line: sub-triangnlar, faintly trilobate pygidium, the 

 annulations of which become obsolescent at maturity ; sur- 

 face pitted. 



Found at '"Hamburg and Eighteen Mile Creek. Erie 

 County." (Hall and Clarke.) It occurs in the lowest Trilo- 

 bite bed, and in the shale below it, down to and in the 

 Pleurodictyum beds of Avery's Ravine. It is a rare form, 

 and no perfect specimens have so far been obtained from 

 this region. 



Genus PHACOPS. Emmrich. 



[Ety. : Pluikos, lens; o])s, eye.] 

 (1839: Emmrich. — De Trilob. Dissert.) 



'"Body oval. Cephalon parabolic: genal angles obtuse, or 

 produced into minute spines. Glabella tumid, prominent, 

 widest anteriorly; the two anterior pairs of lateral farrows 

 indistinct. Eyes very large, con- 

 spicuous, bearing numerous cor- 

 neal lenses. Thorax sub-cjuad- 

 rate; segments eleven: pleune 

 arched, and rounded at their ex- 

 tremities. Pygidium moderately 

 large, composed of few annula- 

 tions: margin entire and not pi'o- 

 longed into a terminal spine." 

 (Pal. N. Y., Vol. VII., p. xxix.) 



PuACOPS EANA. (Greeu. ) ( P^ig. 

 256.) (Pal. N. Y., Vol. VIT., p. 

 19, Pis. VII., VIIL, VIII.A.) 



Distinguishing- Ch n ra cte rs. — 

 Sub-semi -circular outline of 

 cephalon : sub-pentagonal outline ^ „ . „, 



^ 1 r- Fig. 3d6. Phacops rana. A perfect 



of glabella, the posterior furrow specimen (after Hall and Clarke). 



alone distinguishable; prominent, grooved doublure: eyes 

 with forty to fifty lenses; axis of thorax widest al)out 



