CRUSTACEA. 101 



Dimensions. The only entire individual observed is an enrolled specimen 

 from Sandusky, Ohio, having the following dimensions: 



Body. Cephalon. rax. limn. 



Length 78 nun. 121 mm. 34 mm. 23 mm. 



Width 38 mm. .'is nun. 34 mm. 28 mm. 



Observations. Proetus crassimarginatus is not of rare occurrence in detached 

 fragments, in the Upper Helderberg limestone in the Stales of New York 

 and Ohio, but these are usually pygidia, the other parts being seldom seen. 

 Pygidia which are manifestly identical with the limestone species are of common 

 occurrence in the Schoharie grit Figures of such pygidia were erroneously 

 referred to Proetus Conradi in the Illustrations of Devonian Fossils (loc. fit.). 

 A single glabella found in association with these caudal shields agrees with those 

 of the Corniferous limestone specimens. 



Distribution. Upper Helderberg group. Schoharie grit : Schoharie, Scho- 

 harie county ; Knox and near Clarksville, Albany county. Corniferous lime- 

 stone : Clarence and Williamsville, Erie county; Lime Rock, near LeRoy, and 

 Stafford, Genesee county; Phelps and Canandaigua, Ontario county: Port Col- 

 borne and Cayuga, Province of Ontario ; Sandusky, Ohio. 



Proetus folliceps, n. sp. 



PLATE XXIII, FIGS. 3-8. 



General Form and Proportions. Body elongate, outline sub-elliptical, lateral 

 margins nearly parallel. Length to width as 8 to 5. 



Surface convex, anteriorly gibbous, conspicuously and sub-equally trilobate. 



Cephalon short, semicircular, border Hat, moderately broad, horizontal ante- 

 riorly, becoming deflected toward the genal extremities, which are broadly 

 rounded and not produced. Surface very convex, equally trilobate. Length 

 to width as 1 to 2. 



The facial sutures take their origin just within the genal angles, run very 

 obliquely across the occipital ring to the outer angle of the occipital lobes, 

 thence rise abruptly to the eye-lobes and pass, with slight divergence, down 



