394 PALEONTOLOGY OF ILLINOIS. 



before ns this portion of the crown is not preserved. The root is proba- 

 bly short, and of considerable less extent laterally than the crown, with 

 which it is uearly vertical. Lateral diameter of crown .31 inch, eleva- 

 tion of concave face about .17, elevation of convex face .14, lateral 

 diameter of base about .'21 inch. 



The sole representative' of this elegant little form, unfortunately, does 

 uot preserve the entire outline — the basal margin of the concave crown- 

 face and the root having been broken away ; but enough remains for 

 satisfactory description and comparison with other forms, and which 

 ■ exhibit its specific distinctness and also its probable generic identity 

 with Antliodus. It is apparently allied to A. sarcalirfus, N. and W., of 

 the Upper Burlington limestone, the basal outline of the convex crown- 

 face being much as in that form ; but its much more elevated crown 

 and more abrupt declination of the concave face distinguish it from 

 that as well as from other forms of the genus. The above features, 

 together with its symmetrical figure, will readily facilitate the identifi- 

 cation of other individuals, although we have to regret the imperfect 

 condition of the unique example before us, and the lack of a mure com- 

 plete series such as would afford a better knowledge of its specific rela- 

 tions. 



Position and locality : The unique specimen was discovered by Mr. 

 Yan Horne, in the Warsaw beds ; mouth of Piasa creek, Illinois. 



Genus PETALODUS, Owen. 



Petalodus hybridus, St. J. and W. 



PI. XII, Kg. 10. 



We have examined a form of Petalodus represented by two specimens 

 in the collection of Mr. Van Horne, one of which exhibits a nearly 

 entire individual, and the other shows the concave face of the crown in 

 a very satisfactory manner. A cursory examination at first induced us 

 to refer these teeth to P. linguifer, a species originally described by 

 Messrs. Newberry and Worthen, from the Chester formation ; but 

 the acquisition of additional material illustrative of that form, and a 

 detailed comparison with the teeth herein mentioned, seem to prove 

 conclusively their specific distinctness. Hence, in consequence of its 

 apparent resemblance to P. curtus,^. and W., of the Warsaw beds, and 

 the species above referred to, we have designated the present form by 

 the above specific appellation. 



The teeth attain large size. Crown long-elliptical or narrow lozenge- 

 shaped in outline, compressed along the crest and moderately acumi- 

 nate, gradually thickening below; concave face moderately excavated, 



