658 MR. E. R. ALSTON ON NEOTROPICAL SQUIRRELS. [June 18, 



have convinced me that Mr. Allen has laid too much stress on the 

 comparative size of the ears, and length and bushiness of the tail, as 

 distinctive characters. In both these points, as well as in the quality 

 of the pelage, every intermediate stage is often to be found; and I 

 have therefore been obliged to unite Mr. Allen's 8. aureigaster 

 and S. leucops, his S. bootkice and S. hypopyrrhus, and his <S. 

 gerrardi and S. variabilis. On the other hand, I have felt obliged 

 to recognize, at least provisionally, the specific rank of <S. stramineus, 

 S. griseogenys, S. rufo-niger, and 5. pusillus, and more doubtfully 

 that of S. griseoflavus, — thus raising the number of species from 

 ten to twelve. 



In facing the intricate and often baffling problem of distinguish- 

 ing between "species " and "varieties" in such a protean group, I 

 have endeavoured to act in harmony with Mr. Darwin's directions : 

 " When a naturalist can unite by means of intermediate links any 

 two forms, he treats the one as a variety of the other" 1 . It must 

 be remembered that many of these "varieties" apparently breed 

 true and prevail in certain parts of the range ; but all that are here 

 brought together are united by such intergradations that a suffi- 

 cient series at once convinces one of their identity. It is evident, 

 however, that still more complete material will be required before 

 every point can be regarded as definitely settled. 



Before proceeding to remark on the various species 2 , I must 

 return my warmest thanks to all who have assisted me in this in- 

 vestigation, especially to Mr. J. A. Allen, Professor A. Milne- 

 Edwards, Dr. Peters, and Dr. Gunther. 



I. SCIURUS CAROLINENSIS. 



Sciurus carolinensis, Gmelin, Linn. Syst. Nat. i. p. 148 (1788, 

 ex Pennant); Allen, Mon. N.-Am. Rodent, p. 700. 



Length of head and body averaging 10 inches; of tail-vertebrae 

 about 8 inches. 



Upper parts grey or brownish grey, the middle of the back 

 brownish, a rufous lateral stripe usually present ; lower parts white. 

 Tail moderate, washed with white, the hairs yellowish brown or 

 whitish, with narrow black rings, broader black subterminal bands 

 and white tips. 



Hab. Southern Canada ; Eastern United States ; Mexico ; Yu- 

 catan ; Guatemala (?). 



Concerning this well-known Nearctic form I can add almost 

 nothing to Mr. Allen's exhaustive account. He distinguishes three 

 geographical races or varieties, of which two, his " var. caro- 

 linensis" and "var. yucatanensis" are found within the Neotropi- 

 cal limits. The former, smaller and browner than the northern 

 leucotis race, is apparently the S. carolinensis which M. de Saus- 

 sure records from Mexico 3 and Mr. Tomes from Guatemala 4 ; and 



1 Origin of Species, fitli ed. p. 3fi. 



2 The species of which I have been able to examine the types or typical 

 species are distinguished in the following pages by an asterisk. 



3 Rev. et. Mag. de Zool. 18«1, p. 4. ' Proe. Zool. Soc. 1861, p. 282. 



