20 NELSON 



of Mexico and Central America, as against 6 species and 3 

 varieties enumerated by Allen. In the Mammalia of the ' Bio- 

 logia Centrali-Americana,' published in 1880, Alston again 

 recognized 7 species— no more than those mentioned by Lesson 

 in 1842. This wholesale lumping of widely separated species — 

 sometimes under a name inapplicable to any of the forms placed 

 under it — left the group even more complicated than before. 



Dr. Allen followed Alston's paper of 1878 by a 'Synonymatic 

 List of American Sciuri, or Arboreal Squirrels '^ in which he 

 adopted the latter's conclusions. Trouessart, in his ' Revision 

 du Genre Ecureuil'^ in 1880, proposed several subgenera and a 

 few months later enumerated the species in his ' Catalogue des 

 Mammiferes Vivants et Fossiles ' (Rodentia).^ 



During the last 18 years no extended papers on Neotropical 

 squirrels have appeared, but a number of species have been de- 

 scribed from Mexico and Central America by Allen, Thomas, 

 Merriam and myself. 



NOTES ON DISTRIBUTION AND VARIATION. 



Tree squirrels occur in suitable places throughout Mexico 

 and Central America but the distribution of the various species 

 depends largely upon the character of the forests. Thus Sciurus 

 negligens is most abundant in the low, dense forests of ebony, 

 less than twenty-five feet high, on the hot coast plains, while 

 its near relative 5. de^pei loves the shady depths of humid trop- 

 ical forests on the lower mountain slopes where the damp air 

 produces an exuberant tree growth and an abundance of para- 

 sitic plants. The pigmy Sciurus alfari^ first mistaken by its 

 discoverer for a bird — a Dendrocolaptine creeper — also lives in 

 similar surroundings in the mountains of Costa Rica. The 

 large species exist under even more varied conditions since 

 they occur from the hot coast country to the region of oaks and 

 pines close to timberline, but the ranges of different species or 

 subspecies are never coincident and overlap only in a few in- 

 stances, as in the case of ^S*. collicei nuchalis and S. poliopus 



iBull. U. S. Geol. & Geog. Survey Terr., IV, pp. S77-887, 1878. 

 *Le Naturaliste, II, No. 37, pp. 290-293, Oct., 1880. 

 3 Bull. Soc. d'Etudes Sci. d'Angers, X, pp. 76-82, 1S80. 



