CRUSTACEA. 
101 
Dimensions. The only entire individual observed is an enrolled specimen 
from Sandusky, Ohio, having the following dimensions: 
Body. Cephalon. Thorax. Pygidium. 
Length_ 78 mm. 21 mm. 34 mm. 23 mm. 
Width_ 38 mm. , 38 mm. 34 mm. 28 mm. 
Observations. ProHus crassimarginatus is not of rare occurrence in detached 
fragments, in the Upper Helderberg limestone in the States 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 Prottus Conradi in the Illustrations of Devonian Fossils {loc. cit). 
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 flat, 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 
