56 rROCEEDINGS! OF THE NATIONAL MUSEU^I. vol.51. 



point, strong ; hair band on apical part of second abdominal segment 

 interrujoted ; apical region with much pale glistening hair; first 

 posterior cell not appendiculate ; hind tarsi thick, but basitarsi hardly 

 broader than next joint. 



Pupa. — Length 12 mm., width 8, height 5 (female), or length 10.5 

 mm., width 7, height 4.5 (male). Surface sculpture essentially as in 

 31. tr'isfis, figured by Wheeler, except that the space between the mid- 

 most longitudinal raised lines is fully equal to those between these 

 lines and the next, instead of being much less. Color deep red-brown. 



Habitat. — Boulder, Colorado. This is almost certainly the new 

 species recorded from Wet Mountain Valley in 1893. A pupa was 

 found at Boulder a few years ago, but being isolated from its proper 

 environment gave only a crippled male fly, whose wings did not ex- 

 pand. Pupae were found May 1, 1915, in a nest of Formwa rufa 

 aggera/ns "Wlieeler, at Boulder. They were kept in a jar with the 

 ants, and on May 23 a fly of each sex emerged. The specimens 

 described are in the United States National Museum. 



This is certainly allied to M. tristls Loew, but is considerably larger, 

 with the first antennal joint entirely black, the outer angle formed by 

 the first posterior and discal cells larger, thorax above with coppery 

 and brassy (not green or bluish) tints. The dark tibiae and tarsi, 

 and the absence of black pile on the front, show that this is neither 

 M. trktis rufcrus Williston nor 31. tristis cothurnatus Bigot. The 

 last antennal joint is flattened at end, so that it appears obtuse in one 

 view and acute in another. It is probable that it represents a west- 

 ern subspecies of 31. tristis.^ 



'^ Since the above was put in type, Mr. Chas. W. Johnson has published an article in 

 Psyche, vol. 23, June, 1916, p. 75, in which re reviews the subject of M. tristis and 

 cothurnatus. According to the interpretation there given, one Colorado species falls 

 with M. cothurnatus, which is distinct from tristis. 



