194 PALEONTOLOGY OF ILLINOIS. 



and obliquely rounded, with slight sigmoidal outline extending into 

 the posterior alation, which latter is usually broken away. An- 

 terior coronal lobe occupying half or more the breadth of the tooth, 

 gently arched transversely, conspicuously so toward the inner mar- 

 gin, merging into the postero-lateral depression, from which it is 

 defined by the rounded angulation of that side. Surface uniformly 

 and minutely punctate. Length of a medium size tooth along an- 

 tero-lateral border, 19 mm. ; breadth across inner margin, about 

 14 mm. 



Maxillary posterior tooth subspatulate in outline, broadly rounded 

 at inner margin, postero-lateral border slightly concave, gently arched 

 from within outward, extremity not known. Crown surface consider- 

 ably arched transversely over the principal prominence in the vicinity 

 of the inner margin, where the tooth attains comparatively thick, 

 massive proportions, the ridge anteriorly rapidly diminishing in prom- 

 inence. Surface punctation minute and uniform. Length of a tooth 

 below medium size along straight border, probably at least 15 mm. ; 

 breadth, about 9 mm. 



The above descriptions are founded upon a single example of each 

 form, respectively, discovered by Prof. J. J. STEPHENSON. Both speci- 

 mens are in imperfect condition, but such parts as remain present 

 certain peculiarities which seem to justify their reference to a dis- 

 tinct species. Compared with the species prevalent in the Coal Meas- 

 ures of the western States, Orthopleurodus carbonarius, the mandibular 

 posterior tooth differs in the marked transverse convexity of the prin- 

 cipal lobe along the straight side, instead of being flat, as in that 

 form; the opposed teeth of the upper jaw are very like, in both the 

 western and eastern forms, the latter, perhaps, being distinguished 

 by its more massive proportions in the region of the inner margin. 

 A larger suite of material from the Allegheny region may show the 

 above distinctive features to be of subordinate importance, marking 

 mere individual variation, but in a direction not apparent in any of 

 the western specimens. 



Geological position and locality: From strata above Mahoning sand- 

 stone, Coal Measures ; near Morgantown, West Virginia. 



