YEETEBEATES. 3S9 



the collection of Mr. Van Horne, for comparison with that above 

 described. 



Position and locality : Not rare, upper beds of the St. Louis lime- 

 stone ; Alton and Waterloo, Illinois ; St. Louis, Missouri. 



POLYRHIZODUS CARBONARIUS, St. J. and W. 

 PI. X A, Fig. «i, 25. PI. XIII, Fig. 1 



Among the many interesting announcements made during the prose- 

 cution of the present investigations, that of a form of the genus Poly- 

 rhizodus from the Coal Measures of Illinois may claim no inconsiderable 

 share of interest, on account of the extensive stratigraphic range it 

 gives to the genus in the Carboniferous formations of the Mississippi 

 valley, as contrasted with its more restricted range in the Lower Car- 

 boniferous strata of Europe. 



The present form is represented by a very few and imperfectly pre- 

 served individuals, but sufficient to exhibit not only their generic iden- 

 tity, but also their specific characteristics. The teeth are moderately 

 strong, symmetrical, and of medium and large size. Concave crown- 

 face regularly-elliptical in outline, jnore or less deeply excavated, thick 

 below and rapidly attenuated iu the upper portion to the broadly arched 

 crest, lateral angles more or less acutely rounded, basal margin broadly 

 and regularly arched downward, moderately produced, and traversed by 

 a prominent coronal belt of two or three, or more, wide, regular imbri- 

 cations, gradually narrowing towards the lateral extremities; convex 

 face about half the elevation of the opposite side, gently arched later- 

 ally and vertically, sublenticular in outline, basal margin sharply 

 defined, gently arched downward in the median region and broadly 

 curved to the acute lateral angles, basal folds obsolete from attrition, 

 in which condition the entire surface and crest is more or less reduced, 

 and granulo-punctate ; concave face with a polished enamel coating, 

 where it has not been exfoliated by corroding agencies. Base moder- 

 ately strong, as deep again as thick, scarcely more than half the lateral 

 diameter of the crown, slightly obliquely produced, inferior surface 

 well-defined, rounded, deeply divided into seven, more or less, irregular 

 radicles, well-defined from the broad, laterally arched basal area, which 

 is nearly at right angles to the convex crown-face. Lateral diameter of 

 a large tooth 1.35 inch, hight of concave crown-face .50, lateral diame- 

 ter of base about .90, depth beneath the concave coroual border .16. 



The apparent symmetrical proportions and regularity of outline of 

 the present form readily distinguishes it from other described forms. 

 It has some general likeness to P. radicans, McCoy, though it is much 

 less robust in build and the base shorter vertically. The relative pro- 



