1874.] 285 [Allen. 



group rather remarkable for a tendency to melanistic varieties, the 

 black and dusky forms are as often southern as northern. In some 

 species melanistic individuals are as rare as are the cases of albin- 

 ism, as in Sciurus hudsonius, the species of Tamias, and in many of 

 the Spermophili, while in others they are sometimes the common, if 

 not the prevalent, form over a considerable area, as occurs in Sciurus 

 carolinensis and Sciurus cinereus. Melanism is also of frequent occur- 

 rence in Sciurus Aberti, and in Spermopliilus grammurus, which pre- 

 sents a melanistic form both in Texas and Lower California. Sperm- 

 opliilus Parryi has also a black race along the Youkon River, and 

 frequent instances of melanism are well known in all the species of 

 Arctomys. In numerous instances these melanistic individuals and 

 melanistic forms have been described as distinct species, while in re- 

 ality they are generally so sporadic in their occurrence as to render 

 them hardly worthy of recognition, even as varieties. 



The gradual increase of our knowledge in respect to the character 

 of these melanistic forms, and especially in regard to the extent and 

 character of geographical variation, necessarily leads to the modifica- 

 tion of our views in respect to the status of many forms that have 

 formerly passed current as more or less well-established species, and 

 also to consequent changes in nomenclature. The representatives of 

 few groups are more variable in respect to color, even among individ- 

 uals of the same species inhabiting the same locality, than the arbo- 

 real squirrels. Add to this the considerable amount of geographical 

 variation that obtains among them, and the very considerable changes 

 attendant upon season in respect to the character of the pelage, and 

 we shall no longer feel surprised at the profusion of synonyms that 

 attach to many of the species. In respect to the North American 

 members of Sciurus, Prof. Baird, in his excellent monograph of the 

 group published in 1857, found it necessary to reduce the number of 

 species from twenty-four, the number recognized by Audubon and 

 Bachman in 1854, to ten well-established species and two doubtful 

 ones, several of his own species, in this reduction, sharing the fate of 

 those of previous authors. In undertaking recently a monographic 

 revision of the American Sciuridce, I have found it necessary to still 

 further reduce the specific forms to Jive, recognizing, however, seven 

 geographical varieties in addition, making the whole number of rec- 

 ognized forms twelve. As illustrative of the bearing of the class of 

 facts already noticed, I subjoin herewith a synoptical resume of the 

 species and varieties of the Sciuridce of North America found north 



