76 PALEONTOLOGY OF ILLINOIS. 



Belgium, in the De Koninck collection, belonging to the Museum of 

 Comparative Zoology, at Cambridge, bears the manuscript name, 

 Tfeniodus contortus, de Kon ? The characteristics which distinguish 

 this specimen are intimately reproduced in the American samples 

 hereinafter particularly noticed, and which constitute a well-defined 

 form, for which we have adopted the unpublished appellation be- 

 stowed upon the typical species recognized by Dr. de Koninck. The 

 relations of these teeth are apparently near Psephodus, from the 

 supposed maxillary median forms of which they are indeed chiefly 

 distinguishable by the pronounced differentiation of the coronal con- 

 tour, in which respect they approach nearer certain remote forms 

 of typical Cochliodonts, e. g., Stenopterodus. 



The American species are readily distinguishable from the con- 

 generic Belgian species, T. contortus, de Kon. The latter is remark- 

 able for its comparatively strong inrollment, slightly depressed 

 posterior coronal slope; in general proportions and outlines it bears 

 closest reseinllance to the Chester teeth, T. obliquus. 



The genus is known only from Carboniferous strata, of which, 

 besides the typical European representative, there are authentic de- 

 terminations of three species from America, all from the Lower 

 Carboniferous series. 



FACTATUS? (N. and W. sp.) 



PI. XIIT, Fig. 9. 

 Deltodus faciatus. Newberry and Worthon, 1870, 111. Geol. Surv., IV. p. 366, PI. Ill, f, 17. 



Maxillary posterior tooth attaining large size, elongate subhrhom- 

 boidal in outline, gently arched in the direction of inrollment. 

 Antero-lateral border relatively short, obliquely produced outward 

 and forward at an angle of about 25 with a line connecting the 

 inner angles of the tooth; postero-lateral border very gradually 

 converging toward point 'of inrollment with a gently arched course 

 character of coronal fold and basal rim not known in either 

 border ; inner margin making nearly a right angle with the postero- 

 lateral border to a point about midway, where it is abruptly 

 rounded and deflected forward with a slightly concave course thence 

 to the obtuse anterior angle, worn specimens beveled inferiorly. 

 Crown surface chiefly occupied by the posterior prominence, which 

 presents a broad gently convex slope rising from the postero-lateral 

 boarder into the crest, the opposite side more abruptly descend- 

 ing and merging into the shallow depression occupying the anterior 

 portion of the crown; the surface is more or less strongly marked 



