M 



I;i1i 



668 



MONOGUAPOS OF NORTH AMERICAN llODENTIA. 



being two ami a half to three inches iii length. On the other hand, in S. 

 hypopt/rrhus, in which llie length of tiie tail is fully as great as in S.foxsor 

 anil S. co/liai, its breadth is about one-third less. The tail is narrowest (in 

 tlic long-tailed species) in S. astunm, but even in this species it is still dis- 

 tinctly flattened or distichous, except iwssibly in badly prepared specimens, * 

 though not unfrequently cylindrical at the end. 



M- F. Cuvier, in 1818, separated the Guerlinguets from the true Squirrels 

 under the name Macroxux, referring to this group the Sciurus astuans of 

 Brazil and the Sciurus vittatus of India. The characters given for this group, 

 as distinguishing it from Sciurus, are the greater cerebral-capacity of the skull, 

 the tail not distichous at the point, the nasal portion of the skull separated 

 from the cranial by a strong depression, and by the large size of the testes.* 

 Although Afacroxus was adopted by Lesson in 1827, it has been by most 

 writers properly ignored, the characters given having little value. The 

 Macroxus of Gray (1867), although including the species referred to Macroxus 

 by Cuvier, is based on a wholly different feature, namely, on the absence 

 of ear-tufts, and hence embraces all the Sciuri with untufted ears. Sciurus, 

 as left by Gray, thus includes only a few species with conspicuously tufted 

 ears, like iS. vulgaris and S. aherti. This distinction, it is almost needless 

 to say, is not of the slightest importance as a generic character, the long car- 

 tuils being merely a seasonal feature, if not in part, in some species at 

 least, simply individual. In the North American 8. aherti, individuals are 

 found both with and without them at the same localities pnd seasons, while 

 in other individuals they may be found of different degrees of development. 

 Many other species have the ears slightly tufted in winter, which are wholly 

 without ear-tufts in summer. 



The American Sciuri reach their greatest numerical development in 

 Middle America; Southern Mexico and Central America being far richer in 

 species than any other region in either North or South America of similar 

 area. The species are here remarkable also for their extreme variability in 

 color. Melanistic phases of coloration are frequent, while all the species are 

 normally fulvous, orange, or red below, white-bellied specimens from this 

 region being exceptional; with perhaps a single exception, none of the specific 



* The diagnosJB given by Cavier of " lea GaeTliDgneta " ( JfacroxM) Is as follows : — " Ce aont dea 

 6onieuila dont la qaene n'est point dislingntf «t dont la capacity c^ribrale auipaase de beaacoup celle 

 tics dcarenils propremeut dila et celle dcs tamiaa. Une depression trts-marqa^ R<!pare le crtue d'un 

 uiiisenn pea alongd, EuQd, ils sout i-eraariiuablca pur lonra toaticulea Tolumineuz." — (Dkl. M- Jftl., lix, 

 IBiU, 474.) 



