40 NELSON 



rufous reaching up all along the flanks, covering the outside of thighs 

 and back, and confining the gray dorsal area to a median band on lum- 

 bar region and rump ; the top of head and nape black, thinly grizzled 

 with gray, and the tail black thinly washed with gray above, and with 

 ferruginous along middle of under side. A specimen from Pinal de 

 Amoles, Qiieretaro, has the upperparts, including outside of legs, 

 sides of body and upper surface of tail, nearly uniform pale grizzled 

 gray ; the underparts dingy rusty. A specimen from Catemaco, Vera 

 Cruz (approching hypopyrrJuis in intensity) has the same pattern as 

 the one last described, but the breast and inguinal region are grizzled 

 with gray. The width of the red median band on the under side of 

 tail varies and is sometimes nearly or quite replaced by the widening of 

 the black border. This is a common phase in individuals grading to- 

 ward hypopyrrhus. Specimens from northern Vera Cruz, Queretaro, 

 San Luis Potosi, and Tamaulipas are paler or grayer than those from 

 farther south in central Vera Cruz. 



On the east slope of the Cofre de Perote near Jico and Jalapa, 

 Vera Cruz, most of the squirrels are intergrades between aureogastcr 

 proper and frtt mentor. They are even richer ferruginous below than 

 true a?ireo£-aster^ but have the distinct nape and rump patches and 

 tendency to obsolescence of rufous median band on lower side of tail 

 oifrumentor. On account of the rufous underparts these specimens 

 are referred to atireogastcr rather than \.o frii?Jientor\ they combine 

 the characters of the two forms in about equal proportion but dif- 

 fer slightly from either. Squirrels from Lake Catemaco, Vera Cruz, 

 and about Guichicovi, Serabia, and Santo Domingo, Oaxaca, on the 

 Isthmus of Tehuantepec, show intergradation between true aureo- 

 gaster and hypopyrrhiis., and it is frequently puzzling to decide on 

 which side of the line to class them. 



Melanism is common in this species; it is particularly prevalent in 

 some localities and at times entirely replaces the normal phase. A 

 melanistic specimen from Alta Mira, Tamaulipas, has the top of the 

 head and rest of upperparts dark rusty brown, thinly washed with 

 black, darkest over the shoulders ; tail black slightly washed with gray ; 

 entire underparts, including nose and sides of head to eyes, fore feet 

 and legs and hind feet black, and a thin collar of grizzled rusty brown 

 across the under side of neck. A specimen from Forlon in the same 

 state is similar but has a very much heavier wash of black on the back. 

 Very young squirrels show the characteristic color markings. 



Measurements. — Average of 5 adults from Alta Mira : total length 

 509; tail 260; hind foot 66.6. 



