VERTEBRATES. 147 



prominence relatively narrow, culminating about midway of the an- 

 terior half of the coronal region, abruptly descending to the antero- 

 lateral border, gently sloping into the broad, shallow posterior 

 depression, which together with the slightly upraised wing occupies 

 a proportionately wide extent of the coronal area. Surface marked 

 by sub-equal and more or less parallel transverse folds, separated 

 by narrow furrows similar to the opposed mandibular teeth, and 

 conforming to the curvature of the inner margin. A medium size 

 tooth measures in greatest transverse diameter at the inner margin 

 about 11.5 mm; greatest length from posterior angle to outer in- 

 rolled margin, about 16 mm. 



The species above noticed is closely allied to its congeners of the 

 Deltodus undulatus type. The mandibular posterior teeth are, how- 

 ever, distinguishable by their relative great breadth at the inner 

 margin, as compared to the length; the narrow wing expansion re- 

 calls more the condition prevalent in D. occidentalis, from which, 

 however, it may be recognized by its broader, shorter form and 

 undulated coronal surface. The opposed maxillary teeth bear a 

 striking resemblance to D. cingulatus, N. and W., of the Chester 

 limestone, differing, however, in the greater obliquity of the inner 

 margin and, perhaps, the more numerous transverse sulci, producing 

 the banded appearance of the crown surface, while the more widely 

 expanded wing, and the greater obliquity of the inner margin, also 

 serve to distinguish them from D. undulatus, N. and W. ; also, in 

 both forms of the present species the punctae are perceptibly more 

 crowded than is the case in D. cingulatus, and in which respect they 

 again resemble D. undulatus. 



As yet the collections contain very few examples of the teeth above 

 referred to, but these, besides their small size, offer characters which 

 seem to authorize the recognition of their distinct specific standing, 

 although closely allied to the species with which they have been 

 compared. 



Geological position and localities : Warsaw beds : Barrett's Station, 

 St. Louis Co., Mo. ; Madison county, Piasa creek above Alton, and 

 Scott county, 111. 



