VERTEBRATES. 95 



This tooth is generally similar in form and markings to Poecilodus Jonesii, 

 Ag., but is much larger, and the furrow between the two prominences is cen- 

 tral, while in P. Jonesii it is nearest the anterior end. P. ohliquus, McCoy, is 

 also much smaller and the ridges are angular. 



Figure 13 represents a posterior upper? tooth, seen from above — natural size. 



Formation and locality: Keokuk limestone, Warsaw, Illinois. 



Pcecilodus ornatus, N. and W. 



PI. VIII, Fig. 14. 



Teeth flattened, slightly arched, very thin, sub-triangular or 

 trapezoidal in form, the posterior extremity pointed, basal 

 margin sinuous, lateral margins nearly straight; crown surface 

 raised into a low, rounded, sub-central ridge, running nearly 

 parallel with the posterior margin ; from this the surface slopes 

 down gradually to the anterior end on the other side, descend- 

 ing into a broad, shallow furrow, which extends to the posterior 

 border. It is everywhere ornamented with prominent raised 

 lines, nearly parallel with each other and the basal margin, 

 about 3 to every 2 lines in width. The summits of these cari- 

 nse are crenulated, and their slopes transversely striated by a 

 kind of vermicular rugosity. Where the ridges are most 

 widely separated, the unworn enamel is finely tubercular ; 

 where worn, it is dotted by the sections of these tubecles. 

 Length, 1 inch, 6 lines; breadth of imperfect specimen, 1 inch. 



While generally similar to the other species of the group, which includes P. 

 rugasus, Nob., P. obliquus, McCoy, P. Jonesii, Agassiz, etc, it differs from all 

 these in its thin and flattened form, and in the complex character of its orna- 

 mentation. 



Figure 14 represents posterior terminal tooth, natural size. 



Formation and locality: Keokuk limestone, Warsaw, Illinois. 



Genus DELTODUS, N. and W. 



Gen. Char. — Teeth of medium or large size, thick and strong, 

 triangular in outline, more or less arched, sometimes enrolled 



