1906.] Allen, Mammals from Western Mexico, 2 I I 



Four old adults: Total length, 178 (175-181); tail vertebrae, 91 

 (86-98); hind foot without claws, 19; ear from notch, 14. The series 

 from Escuinapa (13 specimens): Total length, 162 (153-181) ; tail 

 vertebrae, 90 (83-98); hind foot, 17; ear, 14. 



The Escuinapa specimens are practically topotypes, the species 

 having been based on specimens from Rosario, about twenty miles 

 north of Escuinapa. 



15. Perognathus pernix pernix Allen. 



Seventeen skins and skulls and 36 specimens in formalin, all 

 collected in the immediate vicinity of Escuinapa, as follows: Jan. 

 6, 7, Feb. 3,5, May 27, June 2,15, July 7, n, 15, 21, 22. Most of the 

 specimens in formalin were collected on Hacienda Island, a few miles 

 west of Escuinapa. 



1 6. Heteromys pictus escuinapae subsp. nov. 



Type, No. 24502, Escuinapa, Sinaloa, Feb. 3, 1904; J. H. Batty. 



Similar to H. pictus Thomas, but somewhat paler and grayer, with the 

 posterior border of the nasals emarginate instead of truncate. Differs simi- 

 larly in coloration from H. plantinarensis (Merriam), and also in smaller size, 

 but agrees with plantinarensis in having the posterior border of the nasals 

 emarginate instead of truncate. 



In winter pelage this form is similar to true pictus, with a series 

 of topotypes of which it has been compared, differing from it only 

 in having the fulvous of the upper parts of a paler shade, and the 

 gray rather more pronounced. When compared in series the two 

 forms are very appreciably different. The same is true when com- 

 pared with plantinarensis, but in either case it would be difficult to 

 distinguish satisfactorily between single specimens by coloration. 

 But pictus and escuinapa are immediately distinguished by the skulls, 

 through the markedly different form of the posterior end of the 

 nasals, which are squarely truncate in pictus and V-shaped or emargi- 

 nate in escuinapcB. This character proves constant in a large series 

 of both forms, a glance at the nasals being sufficient to positively 

 separate them. 



H. p. escuinapa, and probably all the forms of the pictus group, 

 present two well-marked seasonal phases of pelage, so that in com- 

 paring specimens only those taken at corresponding seasons should 

 be compared. The winter pelage, represented by 10 specimens taken 

 in January and February, is paler and more fulvous than the summer 

 pelage, represented by 16 specimens taken in April and May, the 



