290 



imbedded in a piece of brown sandstone, obtained by Professor Hayden from 

 a Cretaceous deposit he lias indicated as No. 5, on Cannon Ball River. 



The specimen with the remains of five large teeth, reduced one-third, is 

 represented in Fig. 24, Plate XVII. The third tooth of the series, preserved 

 entire and separated from the former, is represented in Fig. 23. 



The dentary bone exhibits nothing peculiar in the present condition of the 

 fossil, and appears* not to have differed in any important point from that of 

 Enchodus. 



The teeth differ from those of the latter. .They are proportionately shorter, 

 saber-like, and situated on broad bases, with ah oblique direction to the edge 

 of the jaw. The thick back border is directed inwardly ; the trenchant 

 border forward and outward. The point is cut off in a slanting manner pos-* 

 teriorly. The back part of the crown toward the base and extending on the 

 sides is fluted, but toward the point and trenchant border is smooth. In sec- 

 tion the crown is ovate, with the long diameter 2f lines. The length of the 

 tooth, including its thickened base, is 10 lines; without the base, the crown 

 measures 7 lines. 



Order Malacopteri. 

 Silurid^s. (?) 



XIPHACTINUS. 



XiPHACTINUS AUDAX. 



Under the above name, I described an ichthyodorulite belonging to the 

 collection of the Smithsonian Institution. The specimen was obtained from 

 the Cretacous formation of Kansas, by Dr. George M. Sternberg, United States 

 Army. I supposed it to be the pectoral spine of a large siluroid fish, but 

 according to Professor Cope, who has had the opportunity of examining many 

 remains of fishes from the Cretaceous formation of Kansas, it belongs to a 

 fish of a peculiar family. This he names Saurodontidse, represented by Sau- 

 rocephalus and some other genera. At first the spine was referred- to the 

 last-named genus, but latterly he appears to be in doubt whether it belongs 

 to this or some other nearly allied genus. The specimen is represented in • 

 Figs. 9, 10j Plate XVII, one-third the diameter of nature. 



The spine is unsymmetrical, thus rendering it probable that it belonged to 

 one of the lateral pairs of fins rather than to any of the vertical fins. It is 

 a broad saber-shaped weapon, in its present condition about 16 inches in 



