VERTEBEATES. 169 



lateral border, from which it is separated by a relatively narrow 

 intervening depression, which is bordered on the one hand by the low, 

 narrow alation, and on the other by the abrupt posterior slope of the 

 coronal ridge, the wide anterior slope descending with gentle con- 

 cavity to the narrow raised fold along the antero-lateral border. 

 Surface regularly marked by strong transverse ridges or undulations 

 spaced by narrow grooves parallel with the inner margin, and 

 enveloped in a dense enamel layer, the worn areas showing coarse 

 widely-spaced punctse. Transverse diameter across the inner margin 

 about 8 mm. ; length of antero-lateral border to joint of inrollment, 

 about 4 mm. 



The form above noticed is represented in the collection of Mr. 

 Van Home by a single specimen, the postero-lateral border of which 

 is broken away, so that the entire outline of the tooth is not shown. 

 In general outline and coronal contour, it bears intimate resemblance 

 to a congeneric form of the Upper Burlington, Dcltodopsis (?) convo- 

 lutus; it may, however, be distinguished from that form by the 

 greater obliquity of the anterior portion of the inner margin, the 

 probable greater width and more distinct definition of the posterior 

 alate lobe, and the strong transverse undulations of the crown to 

 which it owes its ornate character. 



Geological position and locality: Warsaw limestone ; north of Piasa 

 creek, above Alton, "Illinois. 



DELTODOPSIS ? BIALVEATUS, D. ? KEOKUK, and D. ? CONVEXUS. 



PL XI, Fig. 15-18. 



Teeth wedge-shaped viewed from above, moderately arched in the 

 direction of inrollment. Lateral borders deep, very gradually con- 

 verging from within outward with a slightly oblique course; basal 

 portion proportionately very deep, channeled above, with a wide 

 slightly inbeveled belt below, terminating in a more or less sharply 

 rounded rim defining the excavated and sometimes longitudinally 

 furrowed inferior surface, defined above by the relatively narrow, 

 rounded, inbeveled enamel fold; inner margin obliquely and gently 

 rounded from the obtuse anterior ( ?) angle to the subacute angle of 

 the oblique border; coronal belt sharply inbeveled to the deep, 

 slightly produced basal portion. Coronal region usually a little 

 narrower than the base, which extends slightly beyond the limits of 

 the enamel fold in the lateral borders, the worn outer surface pre- 

 senting a pimple lateral convexity, but in the middle and toward 

 the inner margin showing more or less distinct, subangular sulci 



