CRUSTACEA. 
93 
pygidium is shorter, the axis being broader and more abruptly elevated, the 
lateral slopes less evenly convex, the pleural annulations more distinct and 
numerous, the posterior border emarginate. In ProlHus Hesione the pygidium is 
much longer and bears more annulations. 
Distribution. Upper Helderberg group. Schoharie grit; Near Clarksville, 
Knox and elsewhere, Albany county; Schoharie, Schoharie county. 
Proetus Hesione. 
PLATE XX, FKiS. 15, 16. 
ProUus Hesione, Hall. Descr. New Species of Fossils, etc., i). 70. 1861. 
ProUns Hesione, Hall. Fifteenth Kept. N. Y. State Cab. Nat. Hist , p. 98. 1S()2. 
Proetus Hesume, Hall. Illusti-ations of Devonian Fossils, pi. xx, figs. 15, 16. 1876. 
Pygidium semi-elliptical, length to width as 2 to 3, Surface axially elevated, 
depressed-convex on the sides. 
Axis relatively narrower than in the associated species of this genus, having 
a width slightly less than one-third the Avidth of the shield on the anterior 
margin; longitudinally arched, margins tapering slowly to a rounded, scarcely 
elevated apex just within the posterior border; composed of ten or eleven 
annulations Avhich have a retral curve over the axial line. 
Pleura depressed near the longitudinal furroAvs, and sloping evenly to the 
border; composed of eight annulations, each of Avhich is distinctly sulcate for 
its entire length, and all terminate abruptly at the marginal sulcus. Border 
broad, evenly sloping, thickened on its inner edge and gently concave. 
Surface faintly pustulose, the pustules being arranged in rows upon the 
annulations and scattered irregularly over the border. Length 15 mm., 
width 21 mm- 
The single pygidium which has served as the type of this species, presents 
characters so unlike those of the associated species that it Avill be readily 
recognized as distinct. From Proetus angustifrons and P. Conradi it differs in its 
longer pygidium and more numerous annulations, and is in some respects allied 
to P.planimarginatus, Meek, of the Upper Helderberg limestone of Sylvania, Ohio. 
