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UNITED STATES NATIONAL MUSEUM BULLETIN 224 



found. "While it is usually stated that the vertex is 

 strongly and characteristically excavated, there are a 

 few exceptions: In Ancylorrhynchus Latreille it may 

 be quite plane ; in Damalini the enlarged and flattened 

 eyes are greatly raised above the vertex and in this 

 group and in some Laphriinae, such as Cerotainia 

 Schiner and Rhopalogaster Macquart, the upper oc- 

 ciput and vertex are posteriorly flared and excavated. 

 The face of Asilidae is 'well filled and is in contrast to 

 the sunken, excavated face of rhagionids and there- 

 vids. It is without the deep and conspicuous lateral 



Text-Figure 2. — The mouth parts of asilids, as illustrated by 

 Nerax interruptus Macquart. Explanation: 1, the epistoma. 2, 

 maxillary palpus. 3, the labrum. 4, the maxillae. 5, the hypophar- 

 ynx. 6, the labium. 



punctures and creases of the mydaids and some taba- 

 nids. The vertical, lateral face grooves in the Asilidae 

 are best developed in the Damalini and in Plesiomma 

 Macquart. There is frequently a well developed tu- 

 bercle or gibbosity over the whole or lower part of 

 the face and a marked tendency toward stout, long, 

 conspicuous bristles above the epistoma. These bris- 

 tles are often called the mystax. The antenna is gen- 

 really placed a little above the middle of the head, 

 and in Dioctrini and Erythropogon White it is placed 

 high above the middle of the head, thus shortening 

 the front. Three antennal segments are present and 

 in the majority of genera there is at least one terminal 

 microsegment, small or large, and sometimes there are 

 two well developed microsegments, in addition to a 

 terminal spine, or bristle, which may be likened to an- 

 nuli. The end segment often has such a spine or bris- 



tle present apically or subapically. In the Asilidae 

 and some others the third segment bears a long, stout 

 bristlelike terminal style or arista. 



Both front and ocellarium usually bear bristles and 

 their position and number are of some value in classifi- 

 cation. A single ocellar pair may become prominent to 

 the exclusion of others, or there may be only stiff pile 

 present. The subepistomal area is the clypeus ; it is 

 usually distinct from the face. Characteristically, the 

 proboscis is straight and usually longer than the head, 

 that is, it extends beyond the anterior boundry of the 

 face, but may be reduced, minute, and short in the tribe 

 Atomosini. In Ancylorrhynchus Latreille its shape is 

 very peculiar, blunt, short, stout, and directed down- 

 ward and backward. In others the direction of the pro- 

 boscis is often characteristic, being held horizontally 

 forward and the presence of a high, dorsal keel is noted 

 in some genera. Again, the apex may be cylindrical, 

 bifid, depressed dorsoventrally or laterally compressed. 

 Hansen (1883) and Melin (1923) give the anatomy of 

 the mouth in detail. The proboscis consists of a stout, 

 usually cylindroid labium, which forms a tube or cyl- 

 inder that is open and slitlike dorsomedially and holds 

 within it the paired, thin-blade, curved maxilla and the 

 unpaired tubular, bristle-beset hypopharynx, the in- 

 terior of which forms the food canal. Piercing of the 

 prey is done with the hypopharynx and enters the prey 

 at the sharp apex. Above these structures, situated 

 dorsally and chiefly toward the base lies the epipharynx 

 (labrum-epipharynx). This is the structure, which 

 constitutes the middorsal keel of the proboscis. The 

 mandibles are quite rudimentary or absent. 



The maxillary palpus lies at the base beside the 

 labium. It is of great significance in the classification of 

 these flies, and in the higher asilids it is reduced to a 

 single segment. In some of the lower forms, there are 

 traces of a third segment. It is interesting to note that 

 in all except the more generalized species the basal seg- 

 ment is hemicylindroid, that is, it forms a hollow hemi- 

 cylinder, or shell, and various stages of partial fusion of 

 this segment to the lower gena are noticeable. Again, 

 the terminal segment in certain groups is perforate at 

 the apex, the opening may be quite large. In 

 Brachyrrhopala Macquart and allies this end segment is 

 swollen and clavate, with one flattened surface, and re- 

 sembles the rhagionid palpus. 



The thorax is stout and the sclerites strong and thick. 

 Generally, stout macrochaetae are present and are often 

 conspicuous, long, and numerous. They are most useful 

 in classification. The pronotum may be short, without 

 anterior ridge, or if such ridge is present, there is a fur- 

 rowlike depression between and the anterior ridge bears 

 the macrochaetae. Prosternum in the lower forms 

 generally dissociated from the lateral propleuron, but 

 fused in many asilids. The mesonotum is gently curved 

 before and behind, usually more abruptly anteriorly 

 and in some cases is as greatly raised and humpbacked 

 as in some empidids. Metathorax small and reduced, 

 but elements lie above as well as below. The ventral 



