2 University of Michigan 



Most of the region is drained by Toyah Creek, which in turn 

 empties into the Pecos River. Part of the work was done in 

 the arid sage lands, the typical west Texas country, and a part 

 in the edge of the Davis Mountains which bound the region 

 studied on the south and west. The vegetation of course is 

 scanty, and as the expedition encountered a very severe drouth, 

 this condition was strongly emphasized. The all prevalent 

 bush is the catclaw acacia, while greasewood, devil thorn and 

 sage, with a few willows and cottonwoods along the larger 

 arroyas and about the few springs, furnish most of the bal- 

 ance. In the mountains small oaks and a few other trees occur 

 at low elevations. Much of the land is quite bare, there are 

 large outcrops of limestone and some igneous rocks, while 

 everywhere, save in a few of the wider valley bottoms, the soil 

 is shallow and stony. 



"The collection of robber flies was made very casually. I 

 was in the region primarily for the Formicidae, and incidental 

 ly collected a considerable number of other Hymenoptera. 

 This led to a more or less careful search for bees, and the 

 continual harassing which they received at the hands of these 

 predaceous Diptera led to the making of the very informal col- 

 lection of the latter." 



List of Species 



Microstylmn morosum Loew. — This species is variable in 

 color from black to light brown. Some authors use the specific 

 name pallens for the brown specimens. Both extremes and 

 intermediate specimens are represented in the collection, so 

 there appears to be no satisfactory way of placing them in two 

 species. It seems advisable to consider all specimens as be- 

 longing to one variable species. The large size, nearly 50 

 miUimeters in total length, the uniformly dark colored wings 

 and closed first posterior cell characterize the species, which 



