130 PALEONTOLOGY OF NEW YORK. 



With P. Row? (including P. marginalis, Conrad), it agrees in (a) the more 

 elongate and slender form ; (h) the character of the ornamentation of the 

 the cheeks; (c) the relatively narrow axis of the thorax; (d) the convex pygi- 

 dial border. It differs from this species in (a) the narrow glabella not encroach- 

 ing upon the frontal border; (b) the much smaller eyes; (c) the broader, more 

 elevated cheeks; (d) the larger cheek-spines; (e) the convex frontal border; 

 (f) the narrower pygidial axis; (g) the absence of the low elevation connecting 

 the apex of the axis with the posterior border. 



With P. Prouti it agrees in the general features common to all these species, 

 but differs in (a) the character of the frontal border ; (b) the shorter cheek- 

 spines; (c) the tangential glabella; (d) the smaller eyes; (e) the narrower 

 pygidium, with fewer annulations. 



The ornamentation in P. Nevada:, consists of fine almost obsolete granula- 

 tions. The crust of the thorax is broken in such a manner as not to show 

 whether there existed an axial row of strong tubercles as in P. Rowi and 

 P. Prouti. 



These details of difference in all these species cannot be satisfactorily repre- 

 sented in life-size drawings. Dependence must therefore be placed upon the 

 descriptions in establishing the limitations accurately. 



Distribution. "Lower horizon of the Devonian limestone; Comb's Peak, 

 Eureka District, Nevada." (Walcott, op. cit.) 



Proetus occidens. 



PLATE XXI, FIGS. 22, 23. 



Proetus occidens, Hall. Descriptions New Species of Fossils, etc., p. SO. 1861. 

 Proetns occidais, Hall. Fifteenth Rept. N. Y. State Cab. Nat. Hist., p. 108. 1862. 

 Pro, tux oceidens, Hall. Illustrations of Devonian Fossils, pi. xxi, figs. 22, 23. 1876. 



This species, so far as known, is represented by only two somewhat imper- 

 fectly preserved Pvgidia. Their outline is semi-elliptical ; length to width as 

 3 to 4 ; surface depressed-convex. The axis has a little less than one-third 

 the width of the shield on the anterior margin, is moderately convex and tapers 

 evenly to an obtuse apex which lies just within the conspicuous marginal 



