My findings agree with those of Nelson in that skulls from Miniatitlan average longer and narrower than those from Altamira, but this seems not to be significant taxonomically because the series from Altamira is, to judge from the material I have seen, somewhat shorter and broader cranially than is "average" for the alleged subspecies _S. a. aureogaster_. For example, series from Metlaltoyuca in Puebla, 3 km. E Axtla in San Luis Potosi, 8 km. NW Potrero and 20 km. NW Piedras Negras in Veracruz, although obtained from localities well within the geographic range of _S. a. aureogaster_ (as outlined by Nelson), all more closely resemble the "topotypes" of _S. a. hypopyrrhus_ in cranial measurements than they do "topotypes" of _S. a. aureogaster_. Conversely, specimens from that part of the range of _S. a. hypopyrrhus_ most remote from the range of _S. a. aureogaster_ (Montecristo, La Venta, and Teapa, all in Tabasco) more closely approximate the Altamiran series in cranial size and proportions than they do the Miniatitlan material. Therefore, my data contradict the statement of Nelson (_loc. cit._) that the skulls of _S. a. hypopyrrhus_ are larger but proportionately narrower than those of _S. a. aureogaster_. The constriction of the auditory bullae alluded to by Nelson as being present in _S. a. hypopyrrhus_ is also present in _S. a. aureogaster_, occurring in both subspecies in varying degrees without correlation with geographic distribution. Actually, the only concrete evidence of geographic variation that I can detect in these animals is a slight increase southwardly in the frequency and degree of melanism, a kind of variation that is unworthy of taxonomic recognition in this species. It seems best, then, to regard the name _Sciurus aureogaster hypopyrrhus_ Wagler as a synonym of _Sciurus aureogaster aureogaster_ F. Cuvier.