174 PALEONTOLOGY OF ILLINOIS. 



outer extremity, enamel fold relatively deep and strongly inbeveled 

 to the channeled basal rim, which is also beveled, in the worn ex- 

 ample to the obtuse inferior edge; postero-lateral or oblique border 

 similarly gently arched, somewhat undulated, converging at an angle 

 of about 30 with the opposite border, enamel fold rounded and 

 inbeveled to the shallow-channeled basal border; inner margin 

 gently arched round the base of the coronal prominence, with slight 

 concavity in passing the coronal depression to the sub-acute poste- 

 rior angle, inbeveled below. Coronal ridge occupying nearly half the 

 anterior coronal area, prominent, gently, convex along the broad 

 crest, steeply sloped into the posterior depression, where it is 

 defined by a slight impressed angulation, posterior alation scarcely 

 elevated along the outer border. Surface punctation comparatively 

 coarse, irregular, the surface toward the inner margin being trans- 

 versely undulated and enveloped in the dense enamel layer. Infe- 

 rior surface gently concave, smooth. Breadth across inner margin, 

 5 mm; greatest length, 10 mm. 



The unique example furnishing the foregoing description shows a 

 nearly entire, though somewhat worn, tooth, representing, perhaps, 

 the posterior form of the left ramus of the upper jaw. Its relations 

 appear to be near Xystrodus, from which, however, it widely departs 

 in the rounded condition of the enamel fold along the straight bor- 

 der, and especially in the coarse, irregular punctae, which show no 

 sign of arrangement in parallel transverse rows. There also exists 

 some likeness to the teeth mentioned under the head of Deltodopsis ( ?) 

 convolutus, from the same formation, so far as relates to the charac- 

 ter of the punctae and appearance of the surface enamel; but the 

 tooth in question is not homologous with the supposed maxillary 

 posterior form of typical Deltoptyckius, as evidenced by the quite 

 different character of the anterior articular border. In outline, the 

 tooth equally resembles Tomodus, as represented by authentic ex- 

 amples of T. convexus, Ag., and this resemblance is even extended 

 to the coronal contour ; but we are not sufficiently familiar with the 

 character of the articular border in the latter genus to be able to 

 determine its exact relations with the form here particularly referred 

 to. It is, therefore, with no certain convictions as to their congen- 

 eric relations that this example is provisionally placed in the above 

 genus. 



Geological position and locality : Upper Burlington limestone, fish- 

 bed; Pleasant Grove, DesMoines county, Iowa. 



