162 PROCEEDINGS OE THE ACADEMY OF 



July 2. 



The President, Dr. Ruschenberger, in the chair. 



Sixteen members present. 



On a new Genus of Extinct Turtles Prof. Leidy stated that 



in a more careful study of the fossil turtles of Wyoming, he had 

 determined that the one he had named Bsena undata belonged to 

 a different genus. Besides other well marked distinctive charac- 

 ters, like the genus Platemys, it possessed an additional pair of 

 plates to the usual number found in the sternum of the emydoids. 

 These plates are intercalated between the hyo- and hyposternals. 

 In Platemys Bullockii they are quadrate. In the new genus they 

 are triangular, and the sutures defining them cross the plastron 

 like a prostrated letter X, from which character it was proposed 

 to name the genus Chisternon. 



On some remains of Cretaceous Fishes. Prof. Leidy called 

 attention to some teeth of fishes from the cretaceous formation, 

 which he described as follows : 



Otodus divaricatus. 



The species is indicated by an entire tooth of peculiar character, 

 submitted to my examination b}*- Dr. William Spillman, of Colum- 

 bus, Mississippi. It was sent to him from Texas, but its exact 

 locality is unknown. It was probably derived from a cretaceous 

 formation. Of known species it resembles most the Otodus semi- 

 plicatus, Minister, of the chalk of Europe, and has likewise consider- 

 able likeness to a tooth from the chalk of France, represented in 

 fig. ii. pi. *76, of Gervais' Paleontologie Francaise. 



The crown forms an elongated demicone with the apex slightly 

 bent forward. The enamel at the base is plicated in front and 

 behind. The lateral denticles are conical and divergent outward 

 and anteriorly. The root is thick, strong and notched, and rises 

 posteriorly above the middle of the length of the tooth. Length 

 of crown in front 13 lines ; base of same external to denticles of the 

 same width. Breadth of root 15^ lines ; thickness 6 lines. 



OXYRHINA EXTENTA. 



A species founded on a number of teeth obtained from the 

 cretaceous formation of Kansas, by Dr. George M. Sternberg, 

 TJ. S. A., and from near Columbus, Mississippi, by Dr. William 

 Spillman. 



The teeth resemble most those of Oxyrhina Mantelli of the 

 English chalk, and differ mainly in the proportionately greater 

 lateral extension of the base of the crown. 



