1915.] Allen, Review of the South American Sciuride. 151 
Finally I cannot close these acknowledgments without expressing my 
sincerest appreciation of the cordial and sympathetic ‘assistance rendered 
me by H. E. Anthony, assistant in Mammalogy, in relieving me of much of 
the drudgery necessarily attending an investigation of this nature, and for 
many suggestions by which I have greatly profited. The photographs used 
in the present connection have been made by the American Museum pho- 
tographer, Julius Kirschner, under Mr. Anthony’s supervision. 
Explanation of Measurements. 
All measurements are in millimeters, unless otherwise stated. 
All external measurements are the collector’s measurements from the specimen 
before skinning, unless otherwise stated. 
Hind foot: c affixed to measurement in the tables of measurements = cum 
ungues, or foot to end of claws; s affixed = sine ungues, or foot to base of claws. The 
length of the hind foot as given in the text includes the claws unless otherwise stated. 
Skull, total length = occipitonasal length; zygomatic breadth = greatest 
breadth at zygomata; interorbital breadth = least breadth of frontals; breadth of 
braincase = at squamoso-parietal suture; length of nasals = greatest length in 
straight line; breadth of nasals = greatest breadth at anterior end; maxillary tooth- 
row = length at crown surface. | 3 
Measurements by different collectors cannot be taken as strictly comparable 
owing to the liability of difference in methods of measuring, except the total length, 
which should be in all cases comparable. When the collector gives only two measure- 
ments, as length of head and body and length of tail vertebre, the total length here 
given is the sum of these two measurements; when the collector gives as measure- 
ments only total length and length of tail vertebra, the head and body length is 
determined by subtracting the latter from the former. Obvious errors in collectors’ 
measurements, due apparently to mistakes in recording them on labels, are sometimes 
corrected if the skins are well made and seem trustworthy for size and proportions; 
otherwise obviously erroneous measurements are wholly discarded. Only measure- 
ments of adult specimens, whether external or cranial, are utilized unless the fact 
of obvious immaturity is stated. 
Measurements of specimens from different localities, when given collectively, 
are indicated as such in the accompanying text. 
The measurements given in the general text are also separately tabulated for 
more convenient reference. 
HistTorRicaL OUTLINE. 
Species and subspecies. 
The first species of squirrel from South America to receive a systematic 
name was Sciurus estuans, named, but only very briefly described, by 
Linné in 1766, from Surinam, and renamed in 1801 by Shaw Myoxus guer- 
lingus. The second species to receive a systematic name was Scvurus 
