SYNOPSIS OF NORTH AMERICAN SYRPHID^ XXI 



<]. Face receding; tboi'ax without niediau dorsal cinereous Hue. 



Xanthogkamma Schiner. 

 ^g. Face strongly projecting below. 



h. Dorsum of thorax with a niediau cinereous line Mesoghapta Loew. 



hit. Dorsum of thorax without such line Sph^ROPHORIA St. F. & Serv. 



The genus Si/r2)hus, as now restri(;ted, presents a remarkable uni- 

 formity in structural characters, and even in markings, ax well as in 

 the fixity of specific cliaracters. A few divergent forms, it is true, as 

 S. (/eniculaUis, are seen, but on the whole the genus is a close one; this, 

 however, has not prevented attempts at subdivision. There are, 

 though, many osculating points among its correlated forms. From 

 Didea, through S. arcuatus lajrponicus, nothing more than specific dif- 

 ferences are found. From Xanthogranima, through A", onarginatum, dif- 

 ferences of even less value appear. Its coalescence with Melanostoma 

 (through 8. simplex^ for instance) has already been touched upon. 

 Other allied genera are Caiahomha and Uiipeodcs, where the differences 

 are almost wholly confined to the male sex. Leucozona is structurally 

 allied, but the pilosity and markings remove it farther. With AUo- 

 {/nqjta, SphoeropJioria, and Mesograpta, tlie relationship is likewise very 

 appar.ent. All these have a more or less elongate abdomen, as in some 

 species of Syrphus, but besides the yellow markings of the thorax the 

 structure of the head is similar in the last two, to which Asarlcina may 

 be added. 



PELECOCERINI. 



The genus Pelecocera shows the nearest relation with the SyrpMni; 

 but the structure of the head removes it so far from the other genera 

 that I prefer to give it an independent place here for the present. 



sPHEGi:N^iisri. 



Small, slender, elongate, thinly pilose species, with more or less yellow 

 mar Kings on head and abdomen. Antennae short, epistoma produced; 

 marginal cell of the icings open, third longitudinal vein straight or gently 

 curved, anterior cross-vein near the base of the discal cell and rectangular, 

 abdomen contracted, towards the base, the greatest width beyond the middle, 

 in outline cluhshaped or spatulate; hind femora, thiclxened. 



h. Epistoma produced anteriorly, in profile deeply concave from antennse to tip; 



third joint of antennie nearly orbicular Sphegina Meig. 



hh. Epistoma produced more downward, in ])rotile slightly concave from antenn;B to 

 tip Neoascia Will. 



This group in America offers well-defined limitations, characterized 

 by the small size, abdomen, and face. It is one of the oldest geolog- 

 ically. 



