Vol. 5] Gidley. — Fossil Mammals from Virgin Valley. 239 



inserted by two large fangs. The crown of p 2 , which is appar- 

 ently half worn away, is entirely clear of the alveolar border and 

 is really braehyodont in form, although it is elongate and the 

 valleys and fossettes are well filled with cement. The difference 

 in form and development of the protoeonnle is an important 

 character which distinguishes this tooth from that of M. calin\a- 

 rius. This cusp is united with the protocone at the triturating 

 surface by a wide isthmus, but is rounded in outline and shows 

 no tendency to unite with the metaconule. There is also no an- 

 terior fold, or crotchet, on the metaconule which leaves the an- 

 terior fossette uninterruptedly confluent with the median internal 

 valley. The form and character of the protoloph is like that of 

 the corresponding tooth of a specimen (no. 583, U. S. National 

 Museum coll.) referred by Leidy to M. insignis, 1 and of species 

 of Pliohippits from the upper Miocene formations. 



This specimen from the Virgin Valley may represent a new 

 species of Merychippus with Protoliippus or Pliohippus affinities. 



Diameters of p 1 , anteropost, 15 mm., transv. 8.5 mm. 



Diameters of p 2 , anteropost. 24 mm., transv. 20? mm. 



MEBYCHIPPTTS, sp. unlet. (2). 



A last upper molar of the right side (no. 10677, Univ. Calif. 

 Col. Vert. Palae.) represents a small species of Merychippus from 

 the Virgin Valley beds. In size this tooth about equals or is 

 slightly larger than the type of M. seversus (Cope), but has not 

 more than one-half the height of crown. 



Diameters of molar, anteropost. 17.5 mm., transv. 17.5 mm. 



Height of crown (outside), 13 mm., (inside) 9 mm. 



MERYCHIPPUS, sp. indet. (3). 



Two other isolated teeth, both upper molars of the right side 

 (nos. 10669 and 10675, Univ. Calif. Col. Vert, Palae.). indicate 

 a fourth species of Merychippus in this collection. They are 

 larger than the last tooth described, and appear to have been, in 

 the unworn stage, comparatively higher and straighter crowned 



i Jour. Acad. Sci., Phila., vol. 7, (2), 1869, p. 29(3, pi. 17, fig. 5. 



This specimen, also with teeth of a very low-crowned type, is from the 

 Niobrara river, Nebraska, and is probably from the middle or lower Miocene 

 formation which is exposed, underlying the upper Miocene, in the vicinity of 

 Fort Niobrara. 



