1895.] NATURAL SCIENCES OF PHILADELPHIA. 269 



PROTOPTYCHUS HATCHERI, A NEW RODENT FROM THE UINTA EOCENE. 



BY W. B. SCOTT. 



[Investigation aided by a grant from the Elizabeth Thompson Fund of the 

 A. A. A.S.] 



Mr. J. B. Hatcher, Curator of vertebrate palaeontology in the 

 Princeton Museum, who is at present (April, 1895) collecting in 

 the Uinta beds, (upper Eocene) of Utah, has lately discovered a 

 small rodent-skull of a previously unknown type, and recognizing its 

 importance, has sent it in to me for examination and description. 

 The skull proves to be of unusual interest and brings to light some 

 very unexpected facts, which I hasten to bring to the attention 

 of students of the rodents. 



The Dentition. — Only the teeth of the upper jaw (fig. 3) are repre- 

 sented in the specimen, the mandible having been lost. The dental 

 formula is: II CO PI M3. As the front end of the rostrum is broken 

 away, only a transverse section of the incisors is visible in the specimen 

 and here they are seen to be rather small and laterally compressed; 

 there is nothing to indicate that these teeth were sulcate. The pre- 

 molar, p4, is of only moderate size, not quite so large as ml. Owing 

 to its somewhat abraded condition, the pattern of this tooth is rather 

 difficult to make out and all that can be clearly seen is a narrow 

 invagination of enamel from the external side, which extends across 

 about half the transverse width of the crown, and on the inner side 

 is an extremely shallow enamel indentation. The first molar a little 

 exceeds in size any of the other cheek-teeth, though there is not 

 much difference between any of the series in this respect. In its 

 present condition of wear, this tooth displays a deep invagination of 

 enamel from the outer side of the crown, and a very shallow one from 

 the inner side, which, however, is distinctly better marked than in 

 the premolar. The second molar is slightly smaller than the first, 

 but of similiar conformation. The third molar, perhaps in conse- 

 quence of the fact that it is less worn than the others, is of a some- 

 what different pattern. In addition to the enamel invagination from 

 the inner and outer sides, it has two low transverse crests, with a 



