50 PALAEONTOLOGY OF ILLINOIS. 



POLYRIIIZODUS DENTATUS, N. and W. 

 PI. Ill, Fig. 10, 10 a. 



Teeth of moderate size, much broader than high, widest at 

 summit; posterior surface of crown linear in outline, with 

 rounded ends, less than half the height of the tooth, termina- 

 ting above in an acute, porous, cutting edge, which is nearly 

 straight throughout; posterior crown face somewhat concave 

 vertically, nearly straight horizontally ; basal ridge prominent, 

 half the height of the crown face, straight in its central part, 

 curved upward to the cutting edge at each end; anterior face 

 of crown nearly as high as posterior, inclined to the vertical 

 axis of the tooth at an angle of about 45°, straight or very 

 slightly arched vertically, gently arched toward each lateral 

 extremity, where it narrows to a point, terminating below in 

 an acute edge, or angle without distinct coronal ridge or folds ; 

 base linear, as high as crown face, to which it is inclined at an 

 acute angle, smooth, concave vertically, arched laterally; root 

 thicker than crown, composed of numerous sub-quadrate radi- 

 cles nearly half the height of the entire tooth. 



It will be noticed that this tooth has a strong family resemblance to those 

 we have described under the names of Chomatodus multiplicatus and C. lori- 

 forrnis, and through them is distinctly connected with the solid rooted Petalo- 

 donts, and yet the root is deeply, almost regularly, divided into numerous 

 distinct radicles. In this respect it is like the following species, more particu- 

 larly to the next one P. ponticulus. To P. porosus, which so closely approaches 

 Polyrluzodus magnus of McCoy, it is allied by its divided root, and the gener- 

 alities of its form ; but its cutting edge and comparatively light and angular 

 profile, render it distinguishable from that species at a glance. With its 

 numerous sub-equal tooth-like radicles this tooth bears considerable resem- 

 blance to the jaw of some mammal with a series of attached teeth ; a resem- 

 blance which has suggested the specific name given it. 



Figure 10 exhibits the posterior face of the tooth; 10 a, is a profile section ; 

 both natural size. 



Formation and locality: Chester limestone, Chester, Illinois. 



