412 PALEONTOLOGY OF ILLINOIS. 



deflected or curved laterally; both coronal surfaces are enveloped in a 

 delicate enamel-like coatiug, through which are discernible minute 

 puuctre, and aloug the worn, triturating surface of the crest compara- 

 tively coarse punctre appear. Basal area smooth, subcordate in outline, 

 in contour very like the concave crown-face, the mesial line being raised 

 into a slight vertical ridge, which is faintly depressed below, and 

 forming a regular convexity with the convex crown-face above ; root 

 unknown. Lateral diameter of crown . 26 inch, vertical diameter of 

 concave crown-face about .28, elevation of convex face about .08, or 

 when entire .10 inch. 



The fragment of tooth upon which the above description is based, 

 and which belongs to the collection of Mr. Van Hoene, presents some 

 anomalous features which we have uot observed in any of the numerous 

 forms of teeth from our Carboniferous deposits, the real nature of which, 

 as well as its generic relations, in consequence of the imperfect condi- 

 tion of the base, we have not been able satisfactorily to determine. 

 It presents, however, a marked resemblance to the typical forms of 

 Feltodus, with which genus it is here provisionally associated. The 

 basal region suggests a comparison with Ghomatodus (Antliodus) trun- 

 catus, Agassiz, from the Carboniferous limestone of Ireland; but its 

 thickened crest and general uniform convexity of the convex crown- 

 face and basal area widely distinguish it from that form. In the great 

 depth and mesial fold of the basal region, and the produced apex, it 

 presents features recalling Petalorhynchus ; but all these resemblances 

 are apparently subordinate to the characters which more strongly sug- 

 gest Peltodus. Unfortunately, the basal portion, together with the root, 

 is not shown in the solitary example here noticed ; it is not improbable, 

 however, the root formed a slight, narrow, taperiug process, originating 

 in the lower part of the depressed median ridge of the basal region, and 

 produced outward in nearly the same plane, or presenting the general 

 characters common to Peltodus. 



Position and locality : In the lower fish-bed of the Chester formation ; 

 Chester, Illinois. 



Peltodus teansversus, St. J. and W. 

 pi. xrn, Kg. 8. 

 Teeth very small, broadly ovate in outline, lateral diameter a little 

 greater than the antero-posterior length. The concave crown-face forms 

 a suboval area, apparently but slightly depressed, basal border strougly 

 arched downward and rounded. The convex face and basal region 

 forms a continuous convexity, the crown being defined from the basal 

 area by an indistinct coronal fold which is slightly arched downward in 



