1915.] Allen, Review of the South American Sciuride. 175 
trum and longer and posteriorly much narrower nasals; the E. boothia, 
melania, thomasi, goldmani, variegatoides, and adolphei groups a shorter and 
broader rostrum, wider and shorter nasals, and a broader skull than the 
hypopyrrhus (= aureogaster) group. The latter are tropical and southern, 
the former subtropical and northern, but they all blend so thoroughly that it 
seems impracticable to attempt to separate Echinosciurus into minor divi- 
sions. At the south Echinoscturus is sharply separated from all of the South 
American squirrels; at the north it is separated by a wide interval, geo- 
graphically and in cranial characters, from either Hesperosciurus or Neo- 
sciurus, and in structural characters from Otosciurus, which ranges south 
into the mountains of northern Mexico. 
Genus Baiosciurus. 
Plate I, Figs. 7-9; Plate VI,- Figs. 6, 7. 
Bavosciurus Nelson, 1899 (subgenus of Sciurus). Type, by original 
designation, Sciuwrus depper Peters. 
Size medium; tail of medium length (about 47% of eh length); color- 
ation uniform grizzled dark rusty or yellowish brown above, grayish white 
with a buffy wash below; tail black fringed with white. Mamme, 6. 
Premolars, ?, p® well-developed; p* small, crown nearly square; cusps 
on outer border of molars well-developed, the cusplets weakly developed. 
Skull broad, dorsal outline low; rostrum short, nasals about 27% of total 
skull length, 86% of interorbital breadth; zygomatic breadth about 58% 
of skull length. 
Range, eastern Mexico, from central Tamaulipas to Chiapas, Guatemala, 
Honduras, and northern Nicaragua. 
Species: 2, with several subspecies. 
Baiosciurus is about twice the size of Tamzasciurus, and about half the 
size of Mesosciurus hoffmanni, taking the skull as a basis of comparison. It 
has 6 mamme, as in Mesosciurus instead of 8 as in Echinosciurus and Tamia- 
sciurus. It is too different from either of these genera in cranial characters 
to require detailed comparison. The quadrate instead of triangular form of 
p’ in Batosciurus is a distinguishing feature. 
Genus Syntheosciurus. 
Text Figs. 17-19; Plate VI, Fig. 1. 
Syntheosciurus Bangs, 1902. Type, Syntheosciurus brochus Baages by 
designation and by monotypy. | 
Size small (about as in Tamiasciurus); tail of medium development, 
