REPORT ON THE DIPTERA COLLECTED BY LIEUT. W. L. CAR- 

 PENTER IN COLORADO DURING THE SUMMER OF 1873. 



By C. E. Osten Sacken. 



A report on the Diptera of tlie Western Territories must necessarily 

 be influenced by the imperfect condition of the dipterology of the Eastern 

 States. It would be premature to describe the numerous new species 

 contained in most of the western collections, when many common Dip- 

 tera in the Atlantic States have not been named or properly identified 

 yet. The task to be performed, under such circumstances, is to single 

 out from such collections the most remarkable forms the description of 

 which is of an immediate interest, to take note of the facts bearing upon 

 the geographical distribution of insects ; and to preserve the rest of the 

 material, carefully labeled, for future detailed study. The accumulation 

 of such collections will, at some future time, render it worth the while 

 to treat the single groups monographically. The indiscriminate working- 

 up of collections, with promiscuous describing of new species, would only 

 increase the already unbearable ballast of synonymy without any real 

 profit to science. 



A few words on the mode of preservation of the collections of Lieu- 

 tenant Carpenter may not be superfluous. Most of the collections of 

 Diptera previously received from the western exploring expeditions were 

 preserved in alcohol, which made them entirely worthless for scientific 

 purposes. 



The i^resent collection was sent to me in small wooden pill-boxes, 

 in which the specimens, well dried, were closely packed together. Al- 

 though, with this mode of treatment, many specimens were broken and 

 most of the antennse lost, still the specimens remain recognizable and 

 afford useful scientific material for the studj' of the geograpical distribu- 

 tion, and even in some cases for description, provided only the speci- 

 mens are numerous enough. The only satisfactory mode of collecting 

 Diptera is to pin them immediately after catching; but as, under some 

 circumstances, this cannot be conveniently done, the mode of collecting 

 used by Lieut. W. L. Carpenter in the present instance is by far pref- 

 erable to alcoholic treatment. 



The collections of Diptera during the summer of 1 873, were principally 

 made at very high altitudes (8,000 to 10,000 feet, some even higher) in the 

 Colorado Mountains. The materials for the geographical distribution 

 of insects which these collections afford are, therefore, of considerable in- 

 terest. The chief character of the fauna of those high altitudes, as might 

 be expected, is a northern one. Nearly all the species which could be 

 identified (as will be seen in the enumeration given below) had been 

 first described from specimens received from the British possessions in 

 North America. I would name, for instance, Hesperinus brevijrons, 

 Walker, which Mr. Kennicott brought from about latitude 05°, on M;ic- 

 kenzie River, and which I found on Mount Washington, above tree-line. 

 It was brought from Fair Play (latitude 38°, elevation 9,000 to 10,000 

 feet). 



The higher the elevation at which the insects were taken, the more 

 this boreal character of the fauna was marked. Lower down, the pecu- 

 36 G s 



