DIPTEKA. 489 



We divide the Notacantha into three principal sections. 



Those of the first Mydasii, Lat. never have teeth or spines 

 in the scutellum. Their body is oblong, and the abdomen forms an 

 elongated and conical triangle. The wings are distant. Their an- 

 tennas, from which we draw their most distinguishing character, are 

 sometimes composed of five distinct joints, the two last of which form 

 a club in some, and the extremity of a cylindrical stem with a subu- 

 late termination in others, and sometimes of three joints, the last of 

 which is largest, almost cylindrical, tapers to a point and is divided 

 into three annuli; thus these organs are always divided into five. 



In some the antennas are much longer than the head, consist of 

 five joints, are terminated in an elongated club formed by the two 

 last, with an umbilicus at the end from which issues a very short 

 seta. The posterior thighs are stout, and dentated or spinous on 

 the inner side. The tarsi have but two pellets. The posterior cells 

 of the wings are complete or closed before the margin, or narrow 

 or elongated, oblique or transverse. 



These Insects compose the genus 



MYDAS, 



Which is divided into two subgenera. CEPHALOCEBA, Lat., where the 

 proboscis is in the form of a long and projecting siphon, and MYDAS, Fab. 

 or My das proper, where that organ, as is usual in this family, terminates by 

 two large lips. 



In the others, the anlennaB are scarcely longer than the head, cy- 

 lindrical, and tapering to a point at their extremity. The tarsi are 

 furnished with three pellets. The posterior cells of the wings are 

 longitudinal and closed by their posterior margin. 



CHIROMYZA, Wied. 



Where the antennae are composed of five well separated joints, the two 

 last of which are the smallest. 



PACHYSTOMUS, Lat. 



Where the antennae are composed of three joints, the last of which is divided 

 into as many rings. 



In the second section, that of the Dccatoma, Lat., we find anten- 

 nae always composed of three joints, the last of which, the longest, 

 without stilet or seta, and divided into eight rings, is clavate in 



3 M 



