358 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I37 



esting facts about the coxosubalar muscle (CS muscle below) and the 

 tergal depressor of the trochanter muscle (TDT muscle below) 

 emerged that seemed to have some bearing on phylogeny and rela- 

 tionships of families.^ These can be summarized as follows : 



1. The bulk of the Nematocera, usually regarded as the more 

 primitive of Diptera, cannot be so regarded. The imagines lack the 

 TDT muscle and have the coxosubalar muscle in a specialized con- 

 dition; these families are comprised in group 2 of table 4. Many of 

 the flies in this group have helicopter-like flight and are notable for 

 the manner in which they dance up and down in swarms. 



2. A small group of Nematocera possess a TDT muscle and, in 

 some cases at least, appear also to have a CS muscle ; these are com- 

 prised in group i of table 4. Crampton et al. (1942) have drawn 

 attention to the fact that in respect of the metanotum the Psychodidae, 

 including Ncmopalpus, are among the most primitive of Diptera.*' It 

 therefore seems possible that the Diptera falling in this group i of 

 table 4 are among the most primitive living today. A more detailed 

 comparison of these forms in all instars and their possible relatives 

 would be worthwhile. On the ground they have a scuttling manner 

 of walking reminiscent of Panorpa (Mecoptera). 



3. All Brachycera and all Cyclorrhapha appear to lack the CS 

 muscle. This is irrespective of the presence or absence of the TDT 

 muscle. These Diptera are in groups 3, 4, 5, and 6 of table 4. 



4. In the Brachycera many families and some large, well-defined 

 segregates, usually given status subordinate to that of family (i.e., 

 subfamily, tribe, etc.), possess a TDT muscle. These are the families, 

 etc., comprised in group 3 of table 4. 



There are, however, a few families and other subordinate segre- 

 gates or isolated genera that lack the TDT muscle ; these are com- 



5 In this discussion, as elsewhere in this paper, I am using the following simple 

 classification of Diptera: 



NEMATOCERA = Orthorrhapha-Nematocera auct. 



BRACHYCERA = Orthorrhapha-Brachycera auct. = Brachycera-Orthorrha- 



pha auct. 

 CYCLORRHAPHA = Brachycera-Cyclorrhapha auct. 

 ASCHIZA 



SCHIZOPHORA = Muscaria auct. 

 Acalypterata = Holometopa auct. = Haplostomata auct. + Cordyluridae. 

 Calypterata = Schizometopa auct. =z Thecostomata auct.-Cordyluridae. 



The Pupipara cannot be regarded as a natural group, and the families therein 

 must be distributed in the Cyclorrhapha. 



^ I have been unable to obtain specimens of Proloplasa or other Tanyderidae 

 in a condition fit for dissection of the musculature. 



