SYNOPSIS Of NORTH AMERICAN SYRPHlD^. 273 



sition, or the inflection of the anterior end, a like tendenr-y toward an- 

 tenna! elongation is usually apparent. Examples of this will be seen 

 in Microdon, Psarm, Paragus, Pipiza, Leprodomyia, Ghnjsogaster, Volu- 

 eella, etc. The converse, however, is not true. 



Moderate or slight plumosity of the arista is of little value in generic 

 distribution. It is disrejrarded in CMlosia, the Brachyopini, and Eris- 

 talis. Abundant plnmo>>ity, on the other hand, is of excellent value in 

 the Volucellini and Sericomyini. In all the other American genera the 

 arista is bare, but among the European genera plumosity also occurs in 

 Psarus, Doros, and Spathjasier. In situation, the arista departs markedly 

 from its usual basal position only in Pelecocera, Nausigaster, and Mera- 

 pioidus. In some of the long-antennsed ChUosini it is more median than 

 basal. 



The front frequently affords excellent characters, both generic and 

 specific, in its length, breadth, convexity, wrinkles, grooves, etc. The 

 position and size of the ocelli, in species of Pyrophccna, SpJioerophoria, 

 and Mesograpta, are of specific value; otherwise their structure and 

 location are nearly uniform. The projection of the frontal process is 

 extremely great in species of Ceria. In the Xylotini and MiJesini i^s 

 size is usually more noticeable than in the remaining groups, and is 

 greater in the male than in the female; its value is only comparative. 



Unlike all the other Diptera cyclorrhapha (except the Pipunculidse), 

 the supra-antennal lunula is fused with the front, and is not inflatable 

 in the process of extrication from the larval enveloi)e. The face sab- 

 serves this purpose, and it is here that we find the greatest diversiy of 

 structui*e. With the exception of Syrphus, Eristalis, and some others, 

 the species in most cases can be distinguished with more or less cer- 

 tainty by the facial profile. The projection of the epistoma finds its 

 greatest development in Ehingia, and only a little less in Crioprora, 

 GriorMna, species of Volueella, etc. In most genera there is a more or 

 less pronounced convexity near the middle, or a little below, but is 

 sometimes obsolete or wanting where the epistoma strongly projects or 

 is receding. The face is apt to differ in shape in the two sexes; usually 

 the less convexity or tubercularity is in the female. This will be more 

 especially observed in species of Chrysogaster and CMlosia, Myiolepta, 

 Pterallastes, and the more Milesia-Uke forms. 



The eyes differ in size and shape very appreciably in different genera, 

 but characters drawn from them are expressed with difficulty, except 

 by the aid of figures. Their hairiness or pilosity is of greater, though 

 always doubtfully generic, value; it may separate species closely allied, 

 as Syrphus rihesii and >S^. torvus, and species of Didea. The following 

 have more or less occular pilosity: Mierodon spp., Chrysotoxum, Psllota, 

 Pipiza, Paragus, CMlosia spp., Leucozona, Catahomha, Eristalis usually, 

 VoluceUa usually, Copestylum, Mallota, sp. Boliosyrphus, and Clirysoclila- 

 mys. It will be noticed that most of the species with an exterior oblique 

 cross-vein have bare eyes. Does their pilosity bear any relation to the 



