NATURAL SCIENCES OF PHILADELPHIA. 



411 



The crown of the tooth is in general outline an oval, wider at one 

 end than the other, the inner border gently convex and entire. 

 The outer border is marked by six shallow notches which are 

 separated by as many sharp, compressed projections. The emar- 

 ginations and denticles are the termini of corresponding grooves 

 and ridges, which radiate from a smooth space along the inner 

 margin of the crown. From this plane the grooves gradually 

 deepen to the margin; the separating ridges are acute, and with- 

 out irregularity or serration. The base or root of the tooth is 

 quite wide. Externally it extends beyond the border of the crown 

 at the notches, and has projections corresponding to the denticles, 

 from which it is separated by a horizontal notch. On the inner 

 side the base extends like a shelf beyond the posterior half of the 

 crown, and is produced backwards beyond its posterior border. 

 The inferior plane is concave in transverse section ; the crown is 

 plane in all directions. 



Length of crown preserved 

 Width of crown 

 Length of root preserved 

 Depth of tooth internally 

 Depth of tooth externally 



M. 



.021 

 .013 

 .022 

 .005 

 .003 



This Ceratodus resembles the species described by Agassiz 

 under the names of C. parvus and G. serratus from the English 

 Trias, but differs from them in the shortness of the tooth-like 

 processes. In none of the described species do I find such a 

 development of the basis on the inner side. 



This species is of interest as introducing the genus to North 

 America. It is dedicated to Dr. Winslow, to whom we are in- 

 debted for its discovery. 



