106 
PALEONTOLOGY OF NEW YORK. 
Axis convex and slightly arched longitudinally, tapering to a broad, blunt 
termination just within the margin. Width equal to one-third the width of 
the shield. The sides are appressed just above the axial furrows, by a series 
of oblique impressions, one upon each annulation. From seven to eleven 
annulations may be counted upon the axis, the first five having an anterior 
inclination near the margins, and a posterior curve over the median region; 
the posterior annulations are transverse. 
The pleurcE are depressed and curve evenly in ah directions to the margins. 
They bear four annulations and traces of a fifth, and these are marked by 
fine impressed lines. All the annulations become obsolete upon the border, 
the articulating ring, however, encroaching upon it. 
Surface smooth, sometimes granulose upon the glabella and segments. 
Dimensions. An average individual affords the following measurements : 
Body. Cephalon. Thorax. Pygidium 
Length_ 29 mm. 12 mm. 9 mm. 8 mm. 
Width_ 20 mm. 20 mm. 18 mm. 15 mm. 
Observations. Proetus clarus appears to be the most abundant species of this 
genus occurring in the Upper Helderberg limestone, although entire examples 
are of extreme rarity. It shows many points of general and detailed similarity 
with the species Proetus Rowi of the Hamilton group, and Proetus angustifrons of 
the Schoharie grit. From the former it may be distinguished by its relatively 
larger cephalon, a glabella very faintly encroaching upon the frontal border, 
smaller eyes, and fewer annulations upon the pygidium. In Proetus angustifrons 
the cephalon is shorter, the anterior extremity of the glabella tangential upon 
the border, the pygidium more convex, its axis broader anteriorly, more de¬ 
pressed and more rapidly tapering, and its ornamentation more conspicuous. 
Distribution. Upper Helderberg group. Corniferous limestone; Stafford and 
Lime Rock Quarries, near LeRoy, Genesee county; Caledonia, Livingston 
county; Clarence, Erie county; Canandaigua, Ontario county; Cherry Valley, 
Otsego county; Schoharie, Schoharie county; Falls of the Ohio. 
