General Notes. 220 



imens. The skull of the type (that of the other .specimen is missing) 

 lacks the mandible and the entire basal part of braincase, though the 

 remaining portion is in fair condition. It has certain peculiarities not 

 shared by any of the live skulls of R. nelsoni: the postorbital processes 

 are broader and heavier, the palate is more arched between toothrows, 

 and the dorsal profile of braincase is less bent downward posteriorly. 

 These cranial characters are, however, quite within the range of normal 

 variation in members of the family. I consequently have no hesitation 

 in regarding the later name nelsoni, as a synonym of diazi. Mr. E. W. 

 Nelson, who examined the specimens with me, is of the same opinion.* 



Measurements of the type specimens (those of R. "nelsoni" in paren- 

 thesis): hind foot, 48.6 (53); ear from crown, 38.6 (37); greatest length 

 of skull, 60.4 (60.6); zygomatic breadth, 2!)+ (30.4); breadth of brain- 

 case, 22.6 (23.4) ; postorbital constriction, 10. (9.8); interorbital con- 

 striction 9.8 (10.0); nasal, 24.4+ (24.8); greatest breadth of both nasals 

 together, 9.8 (10.0); diastema, 16.0 (15.8); length of palate (lateral), 

 7.4 (7.S); width of palate between anterior premolars, 8.0 (7.6) ; width 

 of palate between posterior molars, 10.4 (10.6); depth at middle of 

 palate, 13 6 (14.0); maxillary toothrow (alveoli), 11.6 (12.0). 



Note. — Four specimens (Nos. 1 74-">: > >l — 1 ) collected at Textlananquila 

 on Mount Iztaccihuatl, above Amecameca, and presented to the U. S. 

 National .Museum by Professor Ferrari -Perez, arrived in Washington 

 after this article was in type. They entirely confirm the identity of 

 Romerolagus dinzi and R. " nelsoni " . 



—Gerrit S. Miller, Jr. 



* I ii view of Mr. Nelson's personal acquaintance with the region where the two 

 types were collected I requested him to give me a brief accountof the geography. This 

 he lias kindly done as follows: " The total area occupied by Rnmerolagus appears to be 

 limited to the middle slopes of the volcanos Popocatepetl and Iztaccihuatl. The 

 boundary line between the states of Mexico and Puebla runs along the crests of these 

 mountains in a northerly and southerly course, thus placing the western slopes in 

 Mexico and the eastern ones in Puebla. These mountains are joined by a broad ridge 

 about 12,000 feet high, at each end of which rise the high peaks. The middle slopes, 

 where Roirn rolagus lives, are continuous around both mountains and lie in an area 20 

 miles long, in a north and south direction, and ten miles broad, from east to west. 

 Romerolagus lives permanently only where it has the shelter of the coarse saccaton 

 grass and the areas occupied by this plant are broken by hot slopes on which it can not 

 maintain itself. These breaks are not wide and can be readily crossed by small 

 mammals. The extremely limited area which Romerolagus occupies, and the absolute 

 identity of climatic and other physical conditions within it, appear to preclude the 

 possibility of the existence of more than one local form." 



