256 PALEONTOLOGY OF ILLINOIS. 



however, may not be of permanent occurrence, and faintly grooved or 

 roughened in the same direction ; the upper surface of the posteriorly 

 produced base is not fully exposed, but appears to be gently convex 

 with obscurely, defined median prominence. Crown very prominent, 

 compressed, abruptly constricted basally in front, and consisting of 

 three stout, acutely pointed, trenchant cusps, strongly compressed in 

 front, broadly rounded behind, of which the median one is the largest, 

 regularly and gradually tapering, gently deflected laterally and more 

 strongly recurved, sublenticular in transverse section ; lateral cusps 

 comparatively very strong, compressed with sharp lateral angles rapidly 

 tapering, strongly divergent or laterally deflected and recurved at a 

 considerably greater angle than the median cone, with which they are 

 intimately connected by the elevated intervening crest ; the coronal 

 surface in front is delicately marked with numerous sharp, more or less 

 irregularly disposed costaj, whose extremities along the basal margin 

 are thickened with obscure indications of spinose processes, and which, 

 ascending the coronal prominence, are deflected or converge in the 

 cusps, where they are bifurcated, and towards the apices replaced by 

 implanted costae, which become obsolete before reaching the lateral 

 edges, which latter are smooth and sharp above, but faintly denticular 

 in the sharp intermediate coronal crest ; both surfaces appear to be 

 similarly ornamented, but in the inner face of the principal cusp the 

 costas are more numerous and abruptly terminated in the smooth area 

 bordering the margins. Lateral diameter of base .50 inch, antero-pos- 

 terior diameter .18, greatest hight of tooth .32, elevation of the inter- 

 mediate coronal crests .13 inch. 



Associated with the above Mr. Wachssittth: has found several speci- 

 mens of a minute form of teeth, which offer at first glance a wide con- 

 trast to the tooth described, but which, on more familiar acquaintance, 

 seem to present closer affinities with that specimen than at first suspec- 

 ted. The latter form, which we have designated under the provisional 

 term P. armatus, although variable individually, is chiefly distinguisha- 

 ble from the above by its smaller size, proportionately stronger lateral 

 cones which exceed the dimension of principal cusp, and the presence 

 of intermediate processes, which latter often spring from the inner mar- 

 gins of the lateral cusps. The outer aspect of the coronal cusps are 

 strongly ridged with flexuose costae, which become obsolete in the cones 

 and especially in their inner margins, where they give rise to the deli- 

 cate processes which correspond to the intermediate denticulation of 

 the crest in the first mentioned specimen ; the inner face of the crown 

 is more strongly arched, and apparently quite free from vertical costae, 

 although there are faint indications of striae. The character of the 

 basal region is very similar to the tootli previously mentioned, although 



