230 proceedings of the academy op 



August 15. 

 The President, Dr. E-uschenberger, in the chair. 

 Eight members present. 



August 22. 

 The President, Dr. Ruschenberger, in the chair. 

 Nine members present. 



August 29. 

 The President, Dr. Ruschenberger, in the chair. 

 Fourteen members present. 



Notice of some Extinct Rodents. — Prof. Leidy remarked that 

 Dr. J. Van A. Carter had recently sent to him some remains of 

 rodents discovered in the tertiary deposits near Fort Bridger, 

 Wyoming. Prof. Marsh has ah-eadj- indicated some remains of 

 the same order, obtained from the same locality, which he has re- 

 ferred to a genus under the name of Sciuravus. The characters 

 given are insufficient to determine positively whether the remains 

 I have the opportunity of examining pertain to the same genus, 

 though, from the greater size of the animals they indicate, they 

 clearly belong to different species. 



The remains appear to have belonged to a peculiar genus of the 

 Sciurine family apparently allied to Arctomys. 



The lower jaw is short and deep compared with that of most 

 living rodents, apparently from a shortening of the bone in ad- 

 vance of the position of the molars. To compensate for this 

 reduction in length, and give room for the incisors, they not only 

 extend beneath all the molars, but also above them posteriorly 

 and externally. Prof. Marsh states that in Sciuravus " the incisor 

 extends below the entire molar series." The hiatus in advance of 

 the molars presents an acute edge nearly on a level with the 

 alveolar border, and does not form a deep notch as usual in living 

 rodents. The masseteric fossa does not extend so far forward as 

 usual in most living rodents, except the hares, only reaching be- 

 low the position of the penultimate molar, where it is bounded by 

 a prominent rectangular ridge, as in the Maryland marmot. The 

 principal mental foramen is situated immediately in advance of 

 the position of the first molar. The symphysis at its lower part 

 apparently extended below the first part of the molar series. 



The number of molars is the same as in the squirrels and mar- 

 mots. They are of nearly uniform size, but are proportionately 

 narrower than in the animals just mentioned, that is, the fore-and- 

 aft diameter exceeds the transverse, which is usually the reverse 



[JSTovember 21, 



