62 NELSON 



Characters. — Upperparts of head and body dark yellowish ; outside 

 of legs and feet dark gray, in strong contrast to back; ears behind, 

 rusty; underparts white; tail slender; ears thickly haired and sparsely 

 tufted; pelage thick and soft; under fur long. Teats: p. \ a. | i. \. 



Color. — Winter pelage : Top of nose gray, rest of upperparts, in- 

 cluding sides of neck and flanks, nearly uniform dark yellowish, griz- 

 zled with black ; outside of legs and feet dark gray, slightly paler on 

 toes ; ring around eye whitish ; sides of head dingy yellowish gray ; 

 ears bordered anteriorly with grayish; behind, including small basal 

 patch, rusty ; underparts white ; tail at base like back but washed with 

 grayish white below; rest of tail above, grizzled black and dark yel- 

 lowish, thinly washed with white; below, mainly dark yellowish, 

 grizzled with black, an indistinct narrow black border and thin white 

 edge. Hairs on back black, with sub-basal and subterminal rings of 

 dark yellowish. 



Variation. — The principal variation in the specimens examined is 

 a difference of intensity in the rusty of the ears. 



Meastiremcnts. — Average of four adults from type locality : total 

 length 4S7.5; tail vertebras 247.5; hind foot 66.7. 



Cranial characters. — Premolars y. Skull markedly different from 

 that of typical collia:i. It is proportionately broader with brain case 

 more flattened, interorbital area broader ; rosti'um shorter and heavier ; 

 nasals shorter and much more deeply emarginate posteriorly ; jugal 

 much broader (exceptionally broad) and expanded vertically ; audital 

 bullse larger and scarcely depressed on inner anterior border. Four 

 adult skulls from type locality average: basal length 47.7; palatal 

 length 24.3; interorbital breadth 1S.3; zygomatic breadth 33.2; 

 length of upper molar series 11. 



General notes. — Sciiirus truei is most nearly related to S. collicei 

 from which it may be distinguished by its uniformly dark yellowish 

 back, slenderer tail, and marked skull characters. Mr. Goldman 

 found it inhabiting the fringe of trees along the Rio Mayo and adja- 

 cent foothills, and heard of it in the foothills near Alamos, Sonora, 

 close to the border of Sinaloa, so there is no doubt of its occurrence 

 also in the northern part of this State. It is named in honor of Mr. 

 F. W. True, Executive Curator, U. S. National Museum.. 



Specimens examined. — Four : all from type locality. 



SCIURUS SOCIALIS Wagner. Tehuantepec Squirrel. 



Sciiirus socialis Wagner, Abhandl. math.-phys. CI. K. bayerisch. Akad. 

 Wiss. Miinchen, 11, pp. 501, 504-507, pi. v, 1837 ; Supplement Schreber's 

 Saugthiere, in. pp. 170-171, 1843 ; Gray, Ann. & Mag. Nat. Hist., 3d 

 ser., XX, p. 428, 1867. 



