L06 PALAEONTOLOGY OF NEW YORK. 



is 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 pleura are depressed and curve evenly in all directions to the margins. 

 The} bear lour annulations and traces of a fifth, and these are marked by 

 line 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. 



9 mm 

 Width .20 mm. 



Length 29 mm. 



Observations. Proetus clarus appears to he the most abundant species of this 

 melius 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 Proitus anguslifrons 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 Proitus anguslifrons 

 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. Corn iferous limestone: Stafford and 

 Lime Rock Quarries, near LeRoy, Genesee county; Caledonia, Livingston 

 comity. Clarence. Kric county. Canandaigua, Ontario county ; Cherry Valley, 

 Otsego count} ; Schoharie, Schoharie county; Falls of the Ohio. 



