The Mylagailid*: — Rigcs. 1:83 



Ml AM Kl MINTS. M. 



Length from posterior incisive alveolus to posterior molar surface 023 



Length of inferior molar series 013 



Length of diastema 010 



Anteroposterior diameter of premolar 009 



( Ireatest lateral breadth of premolar 0042 



Greatest lateral breadth of last molar 0035 



Depth of mandible at anterior molar alveolus 017 



Protogaulus hippodus gen. nov. (sp. Cope.) 



In view of the later described relationship of Meniscomys hip- 

 podus* to the mylagaulid phylum, as well as its differences from 

 other members of the genus, it seems desirable for the sake of 

 natural grouping to transfer the species to the Mylagaulida. Upon 

 these grounds it is proposed to create for it a new genus, retain- 

 ing the specific name. The generic characters thus distinguish- 

 ing Protogaulus from Meniscomys are: " Superior molars short- 

 rooted with external face plane ; inferior molar with a prominent 

 median transverse crest ;"t premolar much larger than molars 

 and having the crescents separated by a deep external fissure ; 

 inferior incisor with a wide groove on its external face. 



MEASUREMENTS.! M. 



Length of superior molar series 



Length from base of first superior molar to base of incisor. 



Width between bases of first molars 



Length of first inferior molar 



Depth of ramus at second molar 



008 

 0065 

 002 

 0033 



0050 



Relationship : The relations of Mylagaulus were for some time 

 left in doubt, but eventually Professor Cope proposed for these 

 forms the family Mylagaulidce. As pointed out by him, the 

 marked development of the lower premolar and the characters 

 of its crown present striking similarities to the dentition of cer- 

 tain species of Hystrix, especially H. refossa. But the complete 

 absence of roots, even in the more primitive form, Mesogaulus, 

 together with the dissimilar origin of the angular portion of the 

 mandible, render the suggested relationship improbable. All of 

 these characters are essentially sciuromorph and to that group the 

 Mylagaulidce certainly belong. 



The presence of but three molar teeth and the complete isola- 

 tion of the enamel fossettes were offered as grounds for the erec- 

 tion of the family Mylagaulidtc If these characters were pos- 



♦Proceedings American Philosophical Society, 1878 (-79), p. 67. 

 tCope's Tertiary Vertebrata, p. 829. 



