202 Wortman — Studies of Eocene Mammalia in the 



Limnocyon velox Marsh. 

 Thinoeyon velox Marsh, this Journal, August, 1872, p. 12, Separata. 



The type of this species, figure 76, consists of an almost 

 complete mandibular ramus, containing the canine and pre- 

 molars more or less complete, as well as the roots of the molars 

 and the alveoli for the incisors. The number of the latter 

 cannot be determined with certainty. Professor Marsh stated 

 them as two, but it is more than probable that there were three, 

 with the middle one pushed back out of position. The canine 



76 



77 



Figure 76. — Left mandibular ramus of Limnocyon velox Marsh (type of 

 Thinoeyon velox Marsh) ; side view ; three halves natural size. (Type.) 



is relatively large, recurved, and its surface exhibits very faint 

 traces of the longitudinal grooving seen in L. verus. The 

 first premolar is two-rooted, with an elongate heel as in this 

 latter species. The remaining premolars resemble the cor- 

 responding teeth of L. verus, except that they are much 

 smaller. The molars, of which only the heel of the last is pre- 

 served, have the same relative size and proportions as in the 

 larger species. The jaw is unusually long and shallow, the 

 symphysis enlarged, the inferior dental 

 canal low in position, and the angle con- 

 siderably inflected. 



From the numerous fragmentary speci- 

 mens of this species in the collection, the 

 following points in its structure may be 

 stated : The last superior molar, figure 

 77, has two external cusps, and the antero- 

 external basal cusp of the first upper 

 molar is distinct and prominent; the 

 Figure 77. — Superior occiput is low and broad, the sagittal 

 Sa^toZ^rtlt: ™* weak, and the condyles large and 

 times natural size. divergent ; there is no accessory con- 



dyloid foramen, and the stylomastoid 

 foramen issues upon the inferior surface of the mastoid ; the 

 tympanic is not ossified into an otic bulla, and the base of the 

 skull is broad, as in the Mustelidse ; the position of the posterior 

 lacerated foramen is posterior and external to the periotic, as 



