NO. 1554. A NEW HORNED RODENT— GIDLEY.' 635 



acteristics and proportions of the skeleton of Epigaulus hatcheri. The 

 anin)al, as a whole, seems to have been especially adapted to digging, 

 for which occupation it was far better equipped than any of the 

 gophers. The highly modified feet and unusually small orbits suggest 

 that the animal may have lived almost exclusively under ground. 



Questions of interest naturally arise in regard to the true meaning 

 and possible utility of the great nasal horns. What is their real 

 significance, and of what use could they have been to a burrowing 

 rodent? Since such a development has no parallel in any of the 

 living forms, any attempted solution of these questions must neces- 

 sarily be based on conjecture. They may have been possessed by the 

 males only, and in that event were probably used principally^ as fight- 

 ing weapons. The discovery of more material will probably settle 

 this point, and the question as well of whether the horns are peculiar 

 to certain genera only, or are characteristic of the entire family. In 

 any case they seem intended for use rather than for ornament, for 

 they are strongl}" built and the whole skull is strengthened to resist 

 severe strains placed upon them. The occiput, too, is broadl3' 

 expanded for the attachment of heavy muscles, which would have 

 enabled the animal to use the horns with great power. It seems not at 

 all improbable, therefore, that they were utilized for burrowing. They 

 may well have served as auxilliaries to the great claws to assist in 

 rapid digging. This suggestion is borne out b}- the fact that the 

 horns are closely twinned, making them especially effective as digging 

 implements, and the tips of the nasals show signs of being protected 

 by callosities, at least, if not by a second incipient pair of horns, sug- 

 gesting that the nose often came in contact with the walls of the 

 burrow. 



Conclusions. — It seems evident from the above study that while this 

 extinct group of highlj^ specialized rodents apparently has .some remote 

 affinities to the Castoridae and a somewhat nearer relationship to 

 the Sciuridte, as pointed out by Matthew, the family has a far 

 greater number of characters in common with the Aplodontidte, and 

 shows besides some striking resemblances of general proportions to 

 some of the Asiatic forms of the Spalacidjie. The resemblance to the 

 latter family, however, seems to be due more to modifications of the 

 skeleton for a similar special adaptation to burrowing habits than to 

 any real relationship. In tooth development, the Mylagaulida^ have 

 surpassed in specialization all other families of the Sciuromorpha, and 

 could not have been ancestral to any of the living forms. 



The affinities of the Mylagaulidfe to any of the known fossil forms 

 is somewhat doubtful. Matthew and Peterson have suggested a pos- 

 sible relationship to Euhapsis., but the genus It/uhapsis shows many 

 more characters of the Castoridte, and is more properly referable to 

 that family. 



