VERTEBRATES. 97 



der rapidly converging toward the outer extremity. Median ridge of 

 crown prominent, occupying a nearly central position and well de- 

 fined from the relatively wide anterior belt, which latter presents 

 the characteristic angulation and abrupt face enveloped for the 

 greater part of its depth in the coronal enamel ; posteriorly the 

 slope of the median ridge descends into the broad depression on 

 that side, from which rises the relatively wide posterior expansion 

 or alation. Crown surface densely punctate. A specimen below 

 medium size measures in greatest length from posterior angle to 

 outer extremity about 11.5 m m. ; antero-lateral border about 6.5 

 m m. ; breadth at inner margin 8mm. 



Posterior tooth of upper jaw of the usual spatulate outline, antero- 

 lateral border obliquely truncated from inner angle forward to outer 

 angle, posterior extremity somewhat produced from which the postero- 

 lateral border somewhat rapidly converges toward point of inroll- 

 ment. Posterior prominences occupy half, or a little more, of 

 the coronal area, secondary lobe about one-third the dimensions 

 of the principal ridge, from which it is separated by a deep furrow, 

 and well defined in front from the apparently smooth anterior area 

 which gradually contracts towards the anterior border. Superficial 

 punctation agreeing with that described above. A mature specimen 

 measures in greatest diameter across the inner margin 17 m m. ; 

 greatest breadth across posterior prominence 7mm.; length along 

 antero-lateral border 4.5 m m. 



The present species is made known from a single representative 

 each of the posterior form pertaining respectively to the upper and 

 lower jaws. Neither of these examples is enlire, although they 

 are sufficiently so to permit of a not unsatisfactory comparison with 

 other generically allied forms. The species is most intimately allied 

 to that occurring in the St. Louis formation, Deltoptychius cxpansus; 

 especially is this relationship apparent in the close resemblance that 

 exists between the maxillary posterior forms of the two species. It 

 differs, however, from the latter species in a marked degree in re- 

 spect to the coronal contour of the mandibular posterior teeth, 

 which shows the median ridge well developed and 'defined from the 

 narrow belt in front and the much greater obliquity of the inner 

 margin of the tooth. 



Geological position and localities : From characteristic strata of the 

 Warsaw formation; Clifton, above Alton, and Golden Bluffs near 

 Warsaw, Illinois. 



