VEETEBEATES. 387 



■with the basal area, nearly straight or but slightly arched downward 

 in the median region, and very gently curved towards the lateral 

 extremities; concave face long-elliptical, with sharply rounded lateral 

 angles, moderately excavated, basal border moderately produced and 

 gently arched, imbrications not shown, but apparently forming a com- 

 paratively narrow belt. Basal area narrow, nearly linear, and at right- 

 angles to the convex crown-face, base proper very low, moderately 

 thick, considerably less than the lateral extent of the crown, well-defined 

 from the basal area, as also from the concave coronal margin, inferior 

 surface rounded, and deeply fissured, with nine or ten irregular radicles. 

 The coronal surfaces are enveloped in a polished enamel-like layer, 

 which is more or less abraded by attrition in the convex face, exposing 

 a striato-puuctate structure usually met with in the triturating surface 

 of these teeth. Greatest diameter of crown about .85 inch, hight of 

 tooth .16, elevation of convex crown-face .12, or about half that of the 

 concave face, depth. of base beneath concave basal margin .07 inch. 



A unique example of the present form was discovered by Mr. Van 

 Hoene in the Warsaw beds above the mouth of Piasa creek, which we 

 believe is the only representative of the genus thus far known from that 

 horizon. Its relatively great lateral elongation readily distinguishes it 

 from other described forms, although in shape it bears a close general 

 resemblance to P. Littoni, N. and W., of the St. Louis limestone. Prom 

 the latter form it may be distinguished by its more slender proportions, 

 less massive base, and more numerous radicles, and the outward or 

 downward arched basal margin of the concave crown-face, more acutely 

 rounded lateral extremities, and probably narrower coronal folds of the 

 same side. 



Position and locality : In the escarpment exposure of brown, friable 

 limestone of the Warsaw beds ; in the Mississippi bluffs one mile above 

 the mouth of Piasa creek, Jersey county, Illinois. 



Polykhizodtxs AMPLXJS, St. J. and W. 



pi. xrn, Kg. 13. 



Teeth of medium or large size, strong, unsymmetrical in outline. 

 Crown moderately thick below, compressed to a thin edge along the 

 broadly and somewhat irregularly arched crest; convex face irregularly 

 long-elliptical in outline, produced and attenuated at one or other 

 extremity, regularly converging and acutely rounded at the opposite 

 extremity, gently arched laterally, triturating surface occupying nearly 

 the entire area, and nearly plane vertically, basal margin obtusely 

 rounded, forming a sub-acute angle with the basal area below, more or 

 less broadly and irregularly arched downward from one extremity, and 



