191G.] NATURAL SCIENCES OF PHILADELPHIA. 541 



in their arrangement, being on the same face on the even segments; 

 the ninth and eleventh segments are smaller and lie between the 

 long, verticillate tenth and twelfth segments; thirteenth segment of 

 the fiagellum long, sigmoid, bearing three long hairs at the apex. 

 Wings with the median cross-vein present, connecting M l+2 with 

 .1/.. 



Type of the subgenus, Rhaphidolabis flaveola Osten Sacken. 



The curious pallid fly that I have deemed best to separate from 

 the other species of the genus is anomalous in many respects and 

 may eventually be placed nearer to Tricyphona, where indeed it was 

 provisionally assigned by Needham. 16 It is certainly more distinct 

 from Rhaphidolabis than is Plectromyia which has herein been con- 

 sidered to have subgeneric value. Under these circumstances it 

 may be better to call the genus Plectromyia, that name having 

 page-priority over Rhaphidolabis, but for the present the latter name 

 has been retained. 



The American species of the genus may be separated by the 

 following key: 



1. Antennse 15-segmented; cross- vein m present (subgenus Rhaphi- 



dolabina). (Northeastern United States.) 



flaveola Osten Sacken. 

 Antennse 13-segmented; cross-vein m absent 2 



2. Cell Mi absent (subgenus Plectromyia). (Northeastern United 



States.) modesta Osten Sacken. 



Cell Mi present (subgenus Rhaphidolabis) 3 



3. Cell Rz petiolate 4 



Cell R 2 sessile 6 



4. Wings whitish hyaline with a dark brown, oval stigma. (Eastern 



Rocky Mountain region.) neomexicana Alexander. 



Wings without a clearly denned, dark brown stigma 5 



5. Antennse of the male elongated; Rs long, straight, the distance 



between Sc 2 and the origin of the sector being less than the 



length of the sector. (Western United States.) 



polymeroides Alexander. 



Antennse of the male short; Rs short, arcuated, the distance 



between Sc 2 and the origin of the sector about two times the 



length of the sector. (Eastern United States.) 



tenuipes Osten Sacken. 



6. Coloration grayish brown, the prsescutum with three dark brown 



stripes; abdomen dark brown with paler caudal margins to the 

 segments; wings very pale brown, the radial sector very short, 



arcuated or angulated. (Northeastern United States.) 



cayuga sp. n. 



16 Twenty-third Report of the New York State Entomologist, PL 25, fig. 3, 

 1907. as Amalopis. 



