1902.] Matthew, A Horned Rodent from Colorado Miocene. 297 



propriately bear it. This claw phalange is long, compressed, 

 the proximal facet very little keeled, the distal end slightly 

 fissured but not symmetrically so, and shows no hood at the 

 base. 



The hind foot when set in position on wax shows an un- 

 mistakable twist, the external side being bent down distally 

 as if the animal walked on the outside edge of the foot, turning 

 the claws inward underneath. This may serve to explain the 

 short, stout fifth digit, as contrasted with the long, slender 

 second; a proportion seen also in the armadillo and some 

 other modern Edentates. 



REVISION OF THE SPECIES. 



On comparing the two skulls and three other more frag- 

 mentary specimens from Colorado with five specimens of 

 Mylagauli from Nebraska in the Cope Collection, it appears 

 that a considerable number of species are represented. On 

 reviewing the description of Mesogaulus hallensis Riggs I find 

 that I was in error in identifying it with Mylagaultis nionodon, 

 but its position can hardly be determined until more is known 

 of the milk dentition and the history of the changes in tooth 

 pattern in this curious family. As far as at present deter- 

 minable the characters of the known species are: 



Mylagaulus monodon Cope. Type, a jaw with the enlarged 

 molar and two alveoli posterior to it, from the Loup Fork of 

 the Republican River Valley. A second specimen, a lower 

 tooth froiTL the same locality, referred to it by Professor Cope, 

 is considerably larger. Enamel lakes in four rows. There 

 are seven lakes in the type ; nine in the associated specimen. 

 No cement outside external enamel ring. 



No. 8327 (type). No. 8328 

 Extreme anteroposterior diam. of molar ? 1 1 . s mm. 13-5 mm. 



transverse " " " 6.5 



Anteroposterior diam. of grinding surface 10.5 n 



Transverse .. .> ■' •■ ^ g 



Mylagaulus sesquipedalis Cope. Type, an upper molar, No. 

 8329. Referred specimen a lower molar and incisor and a 

 metacarpal. No. 8330. Both from the same locality as M. 



