VERTEBRATES. 31 



acute, compressed, with sharp lateral edges, anterior surface 

 flattened, middle and basal portions marked with a few coarse, 

 somewhat irregular, sharply prominent strise, summit smooth; 

 lateral denticles two on each side, long, slender, nearly cylin- 

 drical, coarsely striated, and, like the median cone, slightly 

 curved backward. 



It is to be regretted that this very peculiar species is not represented in the 

 collection by more than a single specimen, as it presents some singular anoma r 

 lies of form. The median cone is much compressed, with cutting edges from 

 summit to base, while the lateral cusps are relatively very long, nearly equal in 

 size, and with a circular outline. They are not unlike C. costatus in the form 

 of the central cusps, yet the striation is more irregular. The lateral denticles 

 are much longer and more slender and widely different, in their section. 



Fig. 17, anterior face and section of median cone; natural size. 



Formation and locality : Coal Measures, Posey county, Indiana. 



SYNOPSIS OF PETAL ODONT GENERA. 

 Family PETALODONTID^E, N. and W. 



Teeth compressed, transversely elongated, crown with ante- 

 rior and posterior surfaces enameled, meeting above in a more 

 or less acute-angled edge, bordered below by imbricating folds 

 of enamel, which encircle the crown ; anterior crown-face 

 generally convex; posterior, concave; root more or less devel- 

 oped, sometimes large, sometimes nearly obsolete, bony, rough, 

 tumid. 



1. Genus PETALODUS, Owen. 



" Teeth transversely elongated, much compressed, thin, petal- 

 shaped, cutting edge serrated; base of crown, with several 

 narrow imbricating folds of enamel, descending lower on the 

 posterior than anterior face ; root large, oblong, thin, truncated 

 below; lower edge obtuse, tumid." 



