32 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 97 
collector, with the aid of a canoe, could secure topotypes of all three 
forms in the same day. Norosi, the type locality of norosiensis, is 
situated in the Rio Magdalena Valley at the foot of the Cordillera 
Central. Twenty-five kilometers east, on the opposite shore of the 
Magdalena near the base of the Cordillera Oriental, is La Gloria, 
type locality of variabilis. Forty-five kilometers downstream at the 
mouth of the Cesar is the type locality of splendidus. The genetic 
distinctiveness of norosiensis from the two races on the opposite side 
of the river may be explained on the basis of geographic isolation. 
The Rio Magdalena at this point is hemmed in by the eastern and 
central Andes, its valley is relatively narrow and its main channel is 
much less subject to change than lower down in the flatlands. Though 
the differences which separate variabilis from splendidus are obvious, 
the geographical conditions that keep them separate are less clear. 
It seems, however, that the elbow of the Cordillera Oriental which 
marks the division of the Cesar Valley of the lower Rio Magdalena 
from the valley of the middle Magdalena serves to isolate partially, 
at least, the two forms. 
In the separate discussion under the subspecific headings it has 
been shown that on higher altitudinal levels of the Cordillera Oriental 
where the geographic barriers mentioned become neutralized, these 
three subspecies converge through a series of gradations into one and 
the same thing. Southward, up the Magdalena and eastward onto 
the Cordillera Oriental, variabilis becomes smaller and darker, the 
belly red, to grade into zuliae and tarrae, respectively. S. g. norosiensis 
must become only slightly smaller and darker up the Magdalena along 
the eastern slope of the Cordillera Central and across the Magdalena 
to the western slope of the Cordillera Oriental, to merge with chrysurus 
and zuliae, respectively. The Rio Cesar squirrel, splendidus, on the 
other hand, in continuing up the main course of the Cesar Valley to 
its head, becomes progressively paler and thus diverges even more 
widely from the typical forms of the other two subspecies. What 
occurs along the east bank of the lower Magdalena to its mouth is 
not known. Typical granatensis west of the mouth of the main 
channel is paler than splendidus but appears to be a well-marked local 
form restricted to the ciénagas surrounding the low foothills of the 
northern terminus of the Cordillera Occidental. It is completely 
isolated from all the other races described in this paper. In the Rio 
Cesar, once the valley bed is left for the eastern mountain chain, again 
the squirrels become smaller and darker. In the mountains over- 
looking the head of the Cesar splendidus intergrades with periyae 
which, in turn, intergrades with tarrae. Lower down, on the south- 
western portion of the Sierra de Perij4, it may be confidently assumed 
that intergrading populations of splendidus, variabilis, peryjae, and 
tarrae all occur. 
