In his excellent taxonomic treatment of the tree squirrels of Mexicoand Central America, Nelson (Proc. Washington Acad. Sci., 1:15-110,2 pls., May 9, 1899) recognized three subspecies of red-belliedsquirrels, Sciurus aureogaster aureogaster F. Cuvier, Sciurus aureogasterhypopyrrhus Wagler, and Sciurus aureogaster frumentor Nelson.In his lists of specimens examined, Nelson (op. cit.:42 and 44)assigned certain specimens from "mountains near Santo Domingo"and Guichicovi in Chiapas, and Catemaco in Veracruz, to S. a.aureogaster, and other specimens from the same localities to S. a.hypopyrrhus. I originally attempted to study (identify to subspecies)the series of animals from only three places, but it becameevident that a more extensive study was indicated.
The locality whence the holotype of Sciurus aureogaster aureogasterwas obtained is unknown. Because certain specimens fromAltamira, Tamaulipas, closely resemble Cuvier's figure of the type,Nelson (op. cit.:41) subsequently designated Altamira as the typelocality. Miniatitlan, Veracruz, was designated by Nelson as thetype locality of S. a. hypopyrrhus because Wagler's description ofthe type of that subspecies fitted so well certain of Nelson's specimensfrom that place.
Sciurus a. hypopyrrhus was said by Nelson (op. cit.:43 and 44) todiffer from S. a. aureogaster in darker color, thinner pelage, muchstiffer and more shining dorsal hairs, slenderer tail with blackpredominating, larger and proportionately narrower skull with largerauditory bullae, each bulla being "slightly constricted just in frontof middle." Sciurus aureogaster varies greatly in intensity ofcolor and in color-pattern. Fully 30 per cent of the specimensexamined are in some degree melanistic and approximately 20 per centof them are completely so. Others are more or less brown; the browndulls the usually rufous parts. In many specimens this brown is welldistributed even in the otherwise grizzled areas; in some specimensit is evenly distributed and in others it is in patches. Indeed,scarcely any two "normally" colored specimens are alike. Typically,the intense rufous color characteristic of the underparts in both[Pg 246]S. a. aureogaster and S. a. hypopyrrhus is also present on thecostal region and shoulders. Even this distribution of color is highlyvariable; some specimens (for example No. 23948 KU, from 3 km. E SanAndres Tuxtla, Veracruz) show no rufous dorsally and others (forexample No. 19307 KU, from 20 km. W Piedras Negras, Veracruz) have therufous extending over the legs, sides, and almost all of the dorsumfrom the shoulders to the rump except (in some) for an interruptedmedian strip of grizzled