256 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 109 



anterior margin, with a pair of almost invisible, slightly depressed 

 lines, the pseudosutural foveae, extending from the pits caudad to 

 near the sides of the scutellum. The mesonotum is clothed with 

 short hairs, which may be somewhat enlarged in rows along the 

 foveae. When a color pattern or pattern of pruinose markings is 

 present, the sublateral markings usually have their mesal margins 

 at the foveae and their greatest breadth is usually at lateral extensions 

 toward the mesonotal or lateral suture, which extends midway on 

 each side from the lateral margins of the mesonotum a short distance 

 mesad. The prescutellar area of the mesonotum is more or less 

 flattened and bears a submedian pair of sensory areas. The scutellum 

 is transverse, with a median caudal expansion and bears a number 

 of strong bristles and short hairs. The postscutellum is arched and 

 bare, with a small, deep, glandular depression. The pleura are bare, 

 each divided into a number of sclerites, with a broad membranous 

 cleft on the anepisternum of the mesopleuron, with an anterior 

 spiracle located in the membrane just behind the pronotum and the 

 posterior spiracle located on the metapleural membrane just below 

 the halter. 



The legs are moderately slender, the femora sometimes slightly 

 swollen, not bearing modified spines or scales. At the apex of the 

 fore tibia are a small spur and a tuft of modified hairs, and at the 

 apex of the hind tibia are an anterior spur and two transverse rows 

 of modified spinose hairs. The term "hind tibial comb" includes 

 only the long spines in the distal row and is sometimes useful in 

 classification. The tarsal ratio is the length of the hind basitarsus 

 divided by the length of the second tarsomere, but we have not 

 found it to be of much taxonomic value in this genus. The fourth 

 tarsomere on all legs is usually cylindrical, but in the subgenus 

 Macfiella Fox it is cordiform. The claws are small and equal on all 

 legs, simple in the female and divided at the apices in the male; the 

 empodium is vestigial. 



The wings possess dense microtrichia, and the macrotrichia or 

 long hairs may range from numerous to absent. There is usually 

 a pattern of pale and dark spots or bands, which is of prime im- 

 portance in classification. The costa extends from the base of the 

 wing to half or more than three-fourths of the wing length. There 

 are with rare exceptions two complete radial cells formed by the 

 heavily sclerotized radial branches. The radial cells are usually 

 of subcqual lengths, and the second or distal one is usually broader 

 than the first, which may frequently be slitlike. We use the Tillyard 

 modification of the Comstock-Needham system of wing venation, 

 whereby the branches of the anterior fork are called Mi and M2 and 

 those of the posterior fork M34.4 and Cui, from front to back. We 



