16 U.S. NATIONAL MUSEUM BULLETIN 27 7 



venter. In the female, the eighth sternum extends posteriorly beyond 

 the margin of the tergum and the ninth tergum has randomly placed 

 coarse hairs; the bursal cavity is longer than wide. 



The species placed in this group have been removed from the pre- 

 ceding group, in some cases on a tentative basis, particularly where 

 only the male is known. Other species presently included in the 

 Albicinctus group may belong here but until their females are found 

 their exact placement is questionable. 



The members of this group are found in the circum-Mediterranean 

 part of the Palaearctic and in the Ethiopian region. 



Velutinus group. — The members of this group are small to 

 medium-sized flies with the abdomen broad and rounded. The head as 

 in the other members of the genus is higher than long, the antennae 

 are generally short, oval, rarely being over twice as long as wide. Vein 

 R4 generally branching from R5 well beyond the middle of the cell. 

 Male ninth tergum bilobed, generally extending ventrally to enclose 

 the genitalia from view in the pinned specimen. The aedeagus is 

 generally well developed and is flanked by two aedeagal parameres of 

 variable length, generally but not always shorter than the aedeagus. 

 The bursal cavity of the female is small and triangular. 



This group is generally limited to the Nearctic and Neotropical 

 regions with an extension into the Pacific Island area. 



FENESTRALIS group 



Provisional Keys to Species of the fenestralis Group 



NEARCTIC SPECIES 



1. Antennae long and narrow 2 



Antennae short, pear-shaped 4 



2. Wings hyaline, halter knob white to brown 3 



Wings smoky gray, halter knob yellow-brown .... 9 S. schroederi Krober 



3. Frons shining, halter knob white, legs orange-brown 



cf 9 S. glabrifrons Meigen 

 Frons rugose, halter knob brown to white, legs red-brown 



d^ ? S. fenestralis (Linnaeus) 



4. R4 branching before the middle of cell R5 5 



R4 branching at the middle of cell R5 ? S. aquelonis, new species 



5. R4 branching from before the middle of cell R5 6 



R4 branching from the basal quarter of cell R5 



cf 9 S. breviterminus, new species 



6. Cell R5 narrowing gradually 9 S. undulafrons, new species 



Cell R5 narrowing abruptly at tip 9 S. nidorcaupulus, new species 



PALAEARCTIC SPECIES (MALES) 



1. Wing hyaline 2 



Wing brown or milky white 4 



2. Frons shining, halter knob white 3 



