MODIFICATIONS OF THORAX 59 



the episternum in front of the wing process. The third (SPz), lying behind 

 the wing process, is well developed. 



The mesosternum is hard to define in the mosquito. A pentagonal sternal 

 plate lies between the mesocoxal cavities behind the median ventral extension 

 from the epistema already described. The postcoxal plates (Sz) of the meso- 

 thorax are attached to the posterior parts of its sides, while its posterior angles 

 are prolonged into slender bands that extend outward and upward in front of 

 the metacoxge and become continuous with the lower parts (c) of the metapleura. 

 Hence, this plate would appear to represent both the mesosternum and the 

 metasternum, for otherwise there is no metastemal element. 



The Metathorax. — The third segment of the thorax is difficult to describe. It 

 is not only reduced in size, but the typical structure is so obscured by secondary 

 modifications that it is impossible to say, from a morphological standpoint, what 

 some of the parts are. The tergum (Tg) forms a narrow dorsal bridge between 

 the postnotum (PN^) of the mesotergum and the first abdominal tergum (IT). 

 The upper part of the pleurum carries the halter (W^) the representative of the 

 hind wing. An irregular line (PS 3) extends downward from the wing support 

 (WPs), which may be known, by the corresponding internal ridge, to be the 

 pleural suture, but it divides before it reaches the coxa and incloses an elongate 

 area (c) that carries the coxal articulation. The plate (Eps^) in front of this 

 suture is, of course, the episternum, while at least some part of the surface be- 

 hind it must be the epimerum {Epm^). The structure of this part, however, is 

 so broken up by accessory sutures that the limits of this sclerite can not be posi- 

 tively asserted. The ventral pleural plate (c) is anomalous and may represent 

 the lower parts of both the episternum and the epimerum since it bears the ar- 

 ticulation of the metacoxa (Ca^g), It is connected by a precoxal band with the 

 pentagonal sternal plate, as described under the mesothorax. Behind the epi- 

 merum (Epnig) are two plates (PN^) reflected upon and fused with the an- 

 terior edge of the first abdominal tergum (IT) . A study of other Diptera sug- 

 gests that these two plates together represent the postnotum (postscutellum) of 

 the metathorax, though, on the other hand, they may belong to the first abdom- 

 inal segment. 



The second spiracle is almost surrounded by the metaepisternum, an unusual 

 condition, though it is generally conceded to belong to the metathorax. 



To the preceding discussion of the thoracic structures by Mr. Snodgrass but 

 little need be added. The thorax is remarkably uniform in structure within the 

 Culicidae and but few modifications occur that are of systematic value. In the 

 systematic part of this work we call the most prominent parts of the prothorax, 

 considered by Snodgrass as probably tergal, the prothoracic lobes. These lobes 

 show considerable diversity in different genera. In most of the Culicini the pro- 

 thoracic lobes are small and lateral. In the genus Stegoconops, however, they 

 are large and very prominent, and nearly contiguous upon the dorsum. In the 

 Sabethini a few genera have the lateral lobes well separated but rather promi- 

 nent laterally (Johlotia, Lesticocampa, Prosopolepis) . In most sabethids, 

 however, the prothoracic lobes are large and prominent, contiguous or nearly so, 



