248 Bulletin American Museum oj Natural History. [Vol. XXII, 



Similar in coloration to S. toltecus and 5. borucce, but smaller and with a 

 very differently shaped skull broad and short with a very broad braincase. 



Above yellowish brown, less rufous than S. toltecus or 5". borucce, though 

 not very distinctly different; ventral surface gray; sides of nose pale buffy; 

 feet gray; tail decidedly blackish above, slightly grayish below. 



Measurements. Type, total length, 235; head and body, 140; tail.vertebrae, 

 95 (slightly imperfect) ; hind foot without claws, 32 ; ear from notch, 22. Eight 

 of the largest (adult) males measure, total length, 245 (238-257) ; head and body, 

 138 (133-146); tail vertebrae, 109 (102-111); hind foot, 30 (27-32); ear from 

 notch, 21.4 (19-22). Eight of the largest (adult) females: total length, 248 

 (238-257); head and body, 140 (136-146); tail vertebrae, 108 (102-111); hind 

 foot, 32 (30-34) ; ear from notch, 20 (19-22). An average adult skull (the type) : 

 total length, 34; basal length, 28; zygomatic breadth, 19; width of braincase, 

 14 (in several other skulls, 15). 



Skull. The skull is short and broad, in comparison with the other Mexi- 

 can forms, the interorbital region being especially shortened, forming a very 

 noticeable feature in comparison with S. boruca and S. toltecus. 



'" In 5. vulcani the pelage is soft and full, and not at all bristly, in 

 this respect resembling 5. mascotensis ( = 5. alleni Bailey), but it is 

 darker and more fulvous in coloration, and differs also from this 

 species in the shortness and breadth of the skull, particularly in the 

 short interorbital region and the more abrupt expansion of the brain- 

 case. The young in first pelage are especially darker than the young 

 of 5. mascotensis in the corresponding stages. Compared with the 

 large S. colimcz of the neighboring tablelands, the differences in sizes, 

 coloration, and shape of the skull are striking. 



Represented by 29 specimens, all taken on the Volcan de Fuego 

 at an altitude of about 10,000 feet, July 10 to 28, 1905. They are 

 mostly adults or young adults, but include a small series of young 

 in first pelage. 



20. Reithrodontomys tennis Allen. 



Thirty-nine specimens: Amatlan de Canas, Tepic, 7 specimens, 

 Jan. 4-12; Rancho Palo Amarillo, near Amatlan, 12 specimens. Jan. 

 2-22 ; Ojo de Agua, Tepic, 3 specimens, Feb. 9, 10; Arroyo de Gavalan, 

 Jalisco (on the Tepic boundary), i specimen, Dec. 21; Estancia, 

 Jalisco, 5 specimens, Jan. 30, Feb. 3, 5; La Cienega, i specimen, 

 April 25; Wakenakili Mountains, 2 specimens, April 27, 29; La Laja, 

 T specimen, May 16; Las Canoas, about 20 miles west of Zapotlan, 

 7 specimens, Aug. 6, 13, 15; Los Masos, i specimen. 



A large number of the specimens are immature, especially among 

 those taken in December, January, and February, while those taken 



