90 THE CANADIAN ENTOMOLOGIST. 



The material in the University collection contains numerous speci- 

 mens that must be C. derivatum, but it is only by a process of elimi- 

 nation that this conclusion can be reached. As Mr. Snow states of other 

 specimens : " They seem to belong here, however, better than else- 

 where." These specimens were taken in extreme North-western 

 Nebraska, and in the Big Horn Mountains, in Wyoming. They exhibit 

 all the variations in the markings of the abdomen that Snow has 

 mentioned (Kans. Uni. Quart. Vol. I., 35). Besides these, there are 

 three specimens of both sexes — two taken at Lincoln and one at Har- 

 vard, Nebraska — that differ as follows : The anterior margin of the 

 wings is only very lightly tinged with yellow, whereas in the others they 

 are always very distinctly so ; the abdomen is covered with erect, light- 

 coloured pile, while in the mountain specimens it is provided with only 

 very short black hairs ; the median stripes of the thorax are very distinct, 

 while in the others they are obsolete or entirely wanting ; the four 

 anterior femora are entirely yellow, while in the others there is a distinct 

 black spot near the base. From this I conclude that these specimens 

 are of a different species, which I am quite certain is pubescens, Loew, 

 although the only differences in the descriptions of these two species are 

 that in one there are distinct dorsal vittse and the wings are tinged with 

 brown anteriorly, while in the other these points are not mentioned, and 

 hence, may or may not be present. But from a study of this material, 

 part of which must be derivatum, I am certain that pubescefis and 

 derivatum are both good species, and should stand, no matter how many 

 of the other species of this genus must fall. I am thus enabled to give 

 the following amended descriptions of the two species. 

 C. derivatum, Walker. 



Second joint of antennae one-fourth to one-half as long as third, 

 sometimes shorter than the first ; arista yellowish. Thorax with the 

 median vitta; at all discernable only in the female. Abdomen every- 

 where covered with short sparse black hairs. First segment black, 

 second lateral margin black, except sometimes the posterior corners, the 

 yellow band is very distinctly interrupted, the two parts arcuate and often 

 expanded medially, posterior margin black. Band of third segment more 

 equal in width than first, interrupted or entire, not always reaching the 

 lateral borders, which are mostly black; entire posterior margin expanded 

 in the middle, yellow. The black markings of the fourth segment vary 

 from an anterior uninterrupted band, expanded to include most of the 



