﻿46 PROCEEDINGS OF THE NATIONAL MUSEUM vol. loo 



yellow side stripes on the mesonotum. The principal yellow cross- 

 bands of S. robusta are entire but they are interrupted on nigritarsi. 

 Several of the females of robusta show the fourth tergite partially 

 interrupted and the bands otherwise quite narrow, a character that 

 indicates a linking of the two species, so robusta may be only a form 

 of nigritarsi. Some of the males also indicate this gradation from one 

 to the other. The genitalia are very much alike. S. nigritarsi is typi- 

 cally darker and robusta., as represented by the Alaska specimens, is 

 never as pale as specimens from the United States. Both these species 

 were described in 1930. 



Genus PLATYCHEIRUS Lepeletier and Serville 



Many of the females of this genus are difficult to determine. Nine 

 species are represented, eight by males that are quite readily placed. 



The males that I have determined as clypeatus Meigen agree with 

 my understanding of this species and they also agree with specimens 

 from Europe. The females, 31 in number, are quite variable and may 

 represent more than one species. Those that I have from Europe are 

 so variable that I am not sure which ones are typical. 



There are six specimens of P. angustatus Zetterstedt, all females, all 

 having the typical pointed abdomen and black fifth segment. 



Genus CHRYSOGASTER Meigen 



Subgenus BARBERIELLA Shannon 

 FiGUEE 10, Tc-q 

 Barberiella Shannon, Ins. Insc. Menstr., vol. 10, p. 122, 1922. 



Shannon erected this subgenus for his new species chilosioides, mak- 

 ing it the type, but he included versipellis Williston, described origi- 

 nally as a Chilosia. He also indicated that his alasken^is belonged to 

 the same group but he had only the female before him. G. nigripennis 

 (Williston) also should be included. 



In his characterization Shannon stated that the front is bare, but 

 there are distinct long black hairs on versipellis and Williston so 

 describes them. The most easily distinguished character is the length 

 of the black bristlelike hairs on the second segment of the antennae ; 

 some at least are longer than the length of this segment, especially 

 above. The first vein extends well out along the margin of the wing 

 and thus elongates the stigma. 



It has long been a puzzle to me why Shannon placed versipellis 

 Williston in his new subgenus and failed to include nigripennis Wil- 

 liston. A recent study of the type specimens shows that the identity 

 labels for these two species became interchanged (the museum numbers 

 however were correct) and thus considerable confusion in the identifi- 



