198 U.S. NATIONAL MUSEUM BULLETIN 275 



These remarkable rodents plug the entrances to their burrows with 

 soil, and they are rarely observed above ground. On several occasions, 

 movements of the plug or fresh talus were observed during the day- 

 time, indicating that they are active both day and night. Specimens 

 were obtained with the use of Macabee gopher traps but only after 

 exhaustive efforts because of the unusually hard, resistant nature of 

 the soil. The small diameter of the entrance of the burrow, which 

 was almost always difficult to locate, and the insistence of these 

 mole rats on pushing fresh dirt over the trap, made trapping difficult. 



During the rainy season in the spring, the soils of the coastal plain 

 are relatively soft and easily workable, and diggings of mole rats are 

 widespread. Accordingly, traps can be more easily set, and the yield 

 is greater. Later in the summer, after the soil has hardened, the 

 number of active burrows is greatly reduced, and in some localities 

 collecting mole rats is much more difficult, if not impossible. At this 

 time these soils of the coastal plain become almost impervious. 



It is interesting to note that mole rats occupying the more firmly 

 packed soils of the Cyrenaican Plateau are generally smaller than 

 those living in the softer, more sandy soils of the coastal plain. Selec- 

 tion has apparently favored smaller body size in these areas where 

 digging is more difficult and a smaller diameter of the burrows is 

 desirable. The soils of the Cyrenaican Plateau are probably harder 

 and less sandy than those of the Egyptian littoral farther east, and 

 this differential in hardness of the soil may account for the differences 

 in size of mole rats from the two areas. 



The character of the soil seems to be the most critical factor in 

 the distribution of these burrowing rodents, and vegetative cover and 

 other physical features of the terrain are of secondary importance. 

 One specimen, 325652, from near Agedabia was taken from a series 

 of active burrows in the extremely hard-packed soil near the roadside 

 on a grassy portion of the coastal plain. These grassy areas, most of 

 which contained diggings, were interspersed among the rather dense, 

 shrubby vegetative cover of the coastal plain. Another specimen, 

 325651, was obtained farther inland where the coastal plain is broad 

 and featureless and has a more uniform vegetative cover. This speci- 

 men was obtained during the spring when the recently emerged 

 grasses were lush and green, and the soil, which normally would have 

 been almost impervious, was soft and workable. Near Labrag, three 

 specimens were obtained from the high uplands of the escarpment 

 which forms the northern terminus of the Cyrenaican Plateau. Even 

 though fresh diggings were widespread, the soil here was extremely 

 hard and rocky, and the specimens were obtained only after laborious 

 efforts. A single specimen, 325657, was obtained from the more alluvial 

 soils in the bottom of the Wadi el Kuf where the ground was also 

 nearly impervious. 



