160 PALEONTOLOGY OF ILLINOIS. 



marks an unmistakable approach to the coronal condition of certain 

 forms near Cocldiodus, e. g. Chitonodus Springeri, etc. Of other dental 

 forms which were associated with the above-mentioned teeth of the 

 mandible and upper jaw, respectively, we are at the present time 

 at a loss to determine their character or identity. 



Authentic examples of the forms here associated together have 

 been derived from the Warsaw, St. Louis and Chester formations; 

 certain forms representing mandibular posterior teeth have also been 

 obtained from the Keokuk formation, but their relations with the 

 present genus are not as satisfactorily shown as in the case of the 

 later introduced forms alluded to. Deltodus angustus, N. and W., of 

 the Chester limestone, which was originally described from examples 

 of the elongate posterior teeth of the upper jaw, is regarded as a 

 typical representative of the present genus. 



Through the courtesy of Lord Enniskillen we have had opportunity 

 to compare the American forms with sketches of a large "palate" 

 from the Carboniferous limestone of Oreton in Shropshire, England, 

 which seems to be congeneric with the teeth above grouped together, 

 and the monarch of its kind. Possessing the same outline and gen- 

 eral contour of coronal region attributable to the maxillary posterior 

 teeth of Deltodopsis, the Oreton example is distinguished by its truly 

 gigantic proportions, and, perhaps, also by its relatively narrow 

 jateral diameter and the very steep declivity descending to the an- 

 tero-lateral border. The tooth from which the above mentioned 

 sketch was made represents the posterior angle of the wing rounded, 

 as though from wear. The specimen measures in greatest length 

 nearly 9 centimetres, breadth across the inner margin about 4 cen- 

 timetres. 



DELTODOPSIS AFFINIS, St. J. and W. 



PL XI, Fig. 1. 



The species here alluded to is represented by a solitary example 

 of the posterior tooth of the mandible. Comparison reveals most 

 intimate relationship with the species occurring in the St. Louis 

 formation, Deltodopsis St. Ludovici. It is characterized, however, in 

 contradistinction to that species, by the relatively great breadth of 

 the posterior depression and wing expansion, the narrower and dis- 

 tinctly transversely depressed anterior slope of the coronal promi- 

 nence. The coronal surface is worn, so that the punctse appear 

 somewhat coarser and more regular, while the transverse undula- 

 tions are very like what occurs in the latter species. Length from 



