92 



NELSON 



Variation. — The striking differences in proportions between speci- 

 mens from the lowlands near Monterey and those from the mountains 

 near Miquihuana (alt. 8500 ft.) as shown by the average measure- 

 ments are not accompanied by similar differences in color. The upper- 

 parts are sometimes grizzled brown and vary from that to nearly clear 

 gray. A specimen from the San Pedro Mines, Nuevo Leon, has 

 the upperparts dark yellowish brown, darkest (thinly washed with 

 black) on top of head. The eye is surrounded by a ring of dark 

 buff, the fore feet are washed with buff and the hind feet with grayish 

 white. Another specimen in similar pelage was taken at Miquihuana, 

 Tamaulipas, in June ; a winter specimen from Rio San Juan, Nuevo 

 Leon, is almost as dark but has grayer sides and feet. No signs of 

 melanism seen. 



Measurements. — Average of five adults from vicinity of type local- 

 ity : total length 471 ; tail vertebrae 217; hind foot 60.6. Average of 

 five adults from mountains near Miquihuana, Tamaulipas: total length 

 465 ; tail vertebrae 330.4; hind foot 6^.?>. 



Cranial characters. — Premolars y. Skulls of S. alleni are only 

 distinguishable from those of S. oculatiis by their smaller size. Five 

 adult skulls from region of type locality average : basilar length 

 50.4; palatal length 26.3; interorbital breadth 18.4; zygomatic 

 breadth 33.7; length of upper molar series 10.5. Five adult skulls 

 from near Miquihuana average: basal length 50; palatal length 25.6; 

 interorbital breadth iS.i ; zygomatic breadth 33.7; length of upper 

 molar series 10.3. 



General notes. — Scinrus alleni bears a close superficial resem- 

 blance to S. carolinensis of Texas, but has only a single premolar. 

 From S. o. tohtccc it differs mainly in smaller size, grayer feet and whiter 

 belly. The type of this species came from near Monterey, Nuevo 

 Leon. By a slip of the pen in the original description the type locality 

 was given as Monterey, Tamaulipas. Baird called attention to this 

 squin-el in 1857, '^^iider the name ' Sciurus carolinensis?'?' and gave 

 the essential characters which separate it from S. carolinensis. Sub- 

 sequent authors have referred it to the same species or to 6". arizofi- 

 ensis., but a series in the collection of the Biological Survey shows that it 

 is a well defined species most nearly related to S. oculatus. Neither 

 S. carolinensis^ nor any close relative of that species occurs in 

 Mexico. 



Specitnens exa?nined. — Twenty-two : from Monterey, Linares, Rio 

 de San Juan, and San Pedro Mines, Nuevo Leon ; near Victoria and 

 Miquihuana, Tamaulipas. 



