THE "MYLAGAULIDA —RIG6s. 183 
MEASUREMENTS. M. 
Length from posterior incisive alveolus to posterior molar surface...... .023 
DOR ANTOLOL THOLAY SECTION, (2905 ds done hs Hae ioe bade UE ws E4034 
SME ATER ESAS EC TENA BS Pats SAD aly gia Piaini oaiuig als Uke SOW hw Hato c ote ah a wre .O10 
Dem isteviar didiwicter Ot Premolar.. |... 4. sicsse ve shonliaawe des .009 
Been? Cnteral reacth OF DeTOOIA bcs... sus cates oe elgg bak ed mewn .0042 
PUIEeC PICCr oN OLeAuen Ol last TMGlar. 2 .f0 2 ck crass caueeee nen 0035 
Depth of mandible at anterior molar alveolus....................055 .O17 
Protogaulus hippodus gen. nov. (sp. Cope.) 
In view of the later described relationship of Meniscomys hip- 
podus* to the my/agaulid 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 Wy/agaulide. Upon 
these grounds it is proposed to create for it a new genus, retain- 
ing the specificname. The generic characters thus distinguish- 
ing Protogaulus from Mentscomys are: ‘‘ Superior molars short- 
rooted with external face plane ; inferior molar with a prominent 
median transverse crest ;’+ 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. 
MAR SU LI@TIIL MISE BOTIES Vy.) Ce Oasis wead ce keen ts chiudccdsces 008 
Length from base of first superior molar to base of incisor............ 0065 
MattrmreWect NaSes (tiiist molars. . elk Tale hee dev ce cues 002 
EPR TTS WO IOU ANG ACK Isis asl doe Sue Sed wk Ob eee ve oe 0033 
Speer Orta ict ate SCCOMMIMOIAL sis, > bichs is, i be die wld bis cic alele Weed e dees 0050 
RELATIONSHIP: ‘The relations of Wy/agaulus were for some time 
left in doubt, but eventually Professor Cope proposed for these 
forms the family Alagaulide. 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 Aystrzx, especially 4. 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 sczwromorph and to that group the 
Mylagaulide 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 Mylagaulide. If these characters were pos- 

*Proceedings American Philosophical Society, 1878 (-79), p. 67. 
+Cope’s Tertiary Vertebrata, p. 829. 
