56 H, C. HrcKETT 



process are specifically different, and cannot be described for purposes of 

 recognition. There are one or two " form-types " of this process that seem 

 to have close affinities in certain species, but the conceptions of them are 

 only relative, and there are many intergrading or questionable examples 

 that detract from the possibility of making a systematic determination. 

 In the following species the process seems to have a common character- 

 istic appearance: Hylemijia trichodadyla, H. curvipes, H. cilicrura H. 

 brassicae. H. antiqua, H. seiitarsata; and again, in Pegomyia vjinthemi, P. 

 vanduzeei, P. ruhivora, P. fuscofascioM, P. calyptrata, P. affinis, P. 

 hicolor, and P. genicu ata. In Hylemyia inornata. H. setigera, and H. 

 betanim, the process is very much reduced; in Pegomyia. hiteola the surface 

 is partially ornamented by black tubercles; in Hylemyia pluvialis, H. 

 testacea, and H. depressa, the margins are serrated and toothed. 



The sustentacular apodeme. — The .sustentacular apodeme is a median, 

 rod-like plate which articulates caudoventrad with the chitinous box. 

 At the base of the apodeme. there arises independently a broad, thin, trans- 

 verse plate, which extends ventrad of the chitinous box and whose lateral 

 margins partially envelop and support the plates of the box. The apodeme 

 proper is composed of two clo.sely fused chitinous plates, which assume 

 their normal position within the body in the median plane. The apodeme 

 may be compressed laterally or dorsoventrally in different degrees and 

 proportions. In Hylemyia cilicrura, the apodeme plates become compressed 

 laterally in the ental region as if for the attachment of directing 

 muscles; in the ectal region the plates become compressed dorsoventrally 

 as if for the articulation and leverage of the chitinous box. In Pegomyia 

 connexa, the apodeme has become reduced to a slight transverse plate. 

 (Plate I, A, B, F, and g.) 



The internal lobes. — In the group here presented, the internal lobes 

 comprise two paii's of chitinous structures which are arranged on either 

 side of the chitinous box, in an oblique plane directed cephalad. Due to 

 their comparative po.sition, the lobes are conveniently designated as (1) the 

 caudal, or inner, pair, and (2) the cephahc, or outer, pair. (Plate I, B.j 



The caudal pair of internal lobes arise from the membrane of the genital 

 pouch. These lobes vary enormously in specific shape and .size. In 

 manj^ species they are erect, perpendicular appendages, as, for example, in 

 Pegomyia affinis, P. hicolor, Hylemyia betarum, Anthomyiella pratincola, 

 and Eustalomyia vittipes; in other species they are decumbent, horizontal 

 appendages, as in Hylemyia trichodactyla. H. pluvialis, H. antiqua, H. 

 brassicae, and H. cilicrura. Distinctive forms are to be found in the 

 species Pegomyia luteola, P. ruhivora, P. winthemi, and P. fuscofasciata. 

 Each lobe typically bears one or more bri.stles or tubercles on the anterior 

 margin. In Hylemyia setigera and H. inornata, the setae resemble long, 

 flexible lashes; in Pegomyia geniculata the bristles are sharply bent near 

 the apex; in P. luteola the setae have the form of a ribband or flagellum; 



