420 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



The sternum, however, is very similar to that of Lcpus. The hind 

 foot is nearly as short relatively as it is in RouicroJagus. While 

 I have seen no skins of Pronolagus, yet the fact that it has always 

 been associated with Lcpus or Oryctolagus makes it appear that 

 its external features are not peculiar, which is all the more inter- 

 esting, as the genus with which it has the most skeletal resemblances, 

 Romcrolagus, externally, bears certain resemblances to the pikas. 



Genus ROMEROLAGUS Merriam 



1896. Romcrolagus Merriam, Proc. Biol. Soc. Washington, x, p. 173, 

 December 29, 1896. 



1898. Lagomys Herrera, La Naturaleza, 2d sen, in, p. 80. 



1899. Romcrolagus Major, Trans. Linn. Soc. London, 2d sen, vii, ZooL, 

 p. 514, November, 1899. 



Type. — Rouierolagus nelsoni Merriam. 



Geogrophical Distribution. — West slope of Mount Popocatepetl, 

 Mexico. 



Diagnosis. — Externally, like Pcntalagus; tail none ; ears and hind 

 feet short. Skull entirely leporine, palate long, postorbital process 

 small, consisting of posterior limb only, nasals as in Lepus, audital 

 bullae normal, ec^ual to foramen magnum in size. First lower pre- 

 molar divided into an anterior and a posterior portion by two re- 

 entrant angles, one extending from the external and the other from 

 the internal face to the center of the tooth ; anterior face of first 

 lower premolar without reentrant angles. Sternum essentially as in 

 Ochotona. 



Skull (pis. Lxxviii, la, lb, ic). — The postorbital processes are 

 small, of similar form and position to those of Pronolagus and 

 Coprolagus, but relatively as well as absolutely smaller. The an- 

 terior angle is entirely lacking, so that the process appears as a 

 triangle, one entire side of which is attached to the cranium. The 

 second side is directed outward and somewhat forward. The third 

 side is directed obliquely inward and backward, forming the outer 

 boundary of a posterior notch. 



The interparietal is present as a distinct, separate bone. 



The bony palate in Ronicrolagus is very long, its least length nearly 

 equaling four times that of m^ and equaled in proportional develop- 

 ment only by Pronolagus. Its length measured half-way between the 

 median line and the inner edge of the dental alveoli is very much 

 greater than the greatest width of the two incisive foramina taken 

 together, and also very much greater than the distance between the 

 vertical plates of the palate bones or width of the choanre. The 



