1915.] Allen, Review of the South American Sciuride. | 155 
reduce even the number admitted by Alston and Allen in 1878! The first 
to be added was Microsciwrus peruanus Allen in 1897, followed in 1898 by 
M. mimulus Thomas, Scturus pyrrhinus Thomas, and Sciurus saltuensis 
Bangs. In the following years new species and subspecies were frequently 
added, chiefly by Thomas and the present writer. 
The total number of specific and subspecific names based on South Ameri- 
can species of squirrels prior to the close of the year 1914 is 88, of which only 
one was published prior to the year 1800, and 12 prior to 1850; 15 appeared 
between 1850 and the end of the year 1898, of which 11 (10 of them by Gray) 
date from 1867. Only one new species was described between 1872 and 
1896, but 4 were added in 1897 and 1898. In 1899 were added 8, and in 
1899 to 1914 (both inclusive) 55, of which 20 were described in the single 
year 1914. 
Of the total number of 88 names given to South American squirrels 
prior to 1915, 18 prove to be synonyms or indeterminable, while 3 were 
given to replace preoccupied names. 
Comparison of the resources and viewpoints of 1878 and 1898. 
Prior to about 1865 mammals of any species were usually represented 
in museums by only a few specimens, and never by large series from a single 
locality. The range of seasonal, geographical, and individual variation was 
hence necessarily little known. Soon after this date material began to 
accumulate rapidly in this country, so that it became possible to study suc- 
cessfully each of these questions. It was found that the range of individual 
variation in the commoner species, which could easily be collected in large 
series, was far greater than was commonly recognized; that season and 
locality had a great influence upon the character of the pelage; and that 
different geographical areas usually presented certain distinctive features 
of variation, notably in size and coloration, in correlation with the extent and 
character of divergent conditions of environment; and that the transition 
between local or geographic forms was as gradual and as complete as the 
correlated transition in physical conditions. All this was real progress in 
knowledge. It was found in some instances that the alleged characters of 
forms currently recognized as species were less divergent than the extremes 
in a large series of individuals of the same species from a single locality; and 
that in many other instances supposed species from somewhat distant locali- 
ties completely intergraded in the intervening areas, and that it was more 
logical to treat such forms as ‘varieties’ than as full ‘species.’ This view 
soon met with wide acceptance in America and proved to be the step- 
ping-stone to the present system of trinomial designations for intergrading 
