VERTEBRATES. 287 



cone is well shown in all ; and a specimen from Warsaw exhibits one 

 extremity of the coronal portion nearly entire, also enough of the base 

 remains to render its generic identity with the last noticed form almost 

 certain. 



In general form the present form bears a close resemblance to H.jpli- 

 catilis, being symmetrically proportioned and apparently of nearly the 

 same dimensions. The base appears to be somewhat narrower, its inner 

 margin more attenuated and rather more strongly arched laterally than 

 in the" case of the former species. The coronal crest is sharp along the 

 lateral portions, and produced into a strong, regularly tapering median 

 cusp, which is slightly compressed, with sharp lateral edges extending 

 half way to the apex. The basal portion of the crown is slightly exca- 

 vated in front, and the lateral and median portions are ornamented with 

 fine, angular, thread-like vertical cost:e, which become coarser near the 

 extremities, obsolete in the upper half the median cone and more nume- 

 rous and crowded in front than behind. Lateral diameter of medium- 

 sized specimen about . 45 inch, hight . 38. 



Associated with the above teeth, there occurs a form which possesses 

 peculiarities which seem to indicate a distinct species, which we have 

 provisionally designated by the name Hybocladodus intermedins, on 

 account of its relationship to H. plicatilis of the Upper Burlington. 

 Particularly is this relationship displayed in the wide base, the poste- 

 rior expansion of which is even greater than in the latter form. The 

 median cone approaches near that of IE. tenuicostatus ; and, while the 

 ornamentation of the crown is coarser than observed in the latter, the 

 costte are more regular and widely spaced than in the former species. 

 The two imperfect specimens representing the form here alluded to, 

 show only enough to render doubtful their identity with either of the 

 forms above mentioned, though not sufBcient to enable a satisfactory 

 elimination of their specific characters. 



Position and locality : Fish-bed horizon of the Keokuk limestone ; 

 vicinity of Warsaw, Illinois, Keokuk and Bentonsport, Iowa. 



Hybocladodus compresstjs. 



PI. V, Fig. 8. 



Bdodus comprei&us, Ueweerkt and WoimiEX, 1860, Geo]. IU. II., p. 78, PI. V, Fig. 1 ; not Helodus 

 compressus, N. and W., vol. iv, p. 360, PI. Ill, Fig. 15. 



Teeth small. Crown autero-posteriorly compressed, and remarkable 

 for the laterally deflected, stout, low, obtuse median cone ; besides the 

 crest is suddenly compressed to a thin edge, interrupted by faint ser- 

 rations, and laterally produced at an acute angle beyond the base; the 

 body of the outer face is occupied by short, nearly vertical plicte, while 



