344 INSECTA. 



The posterior tliighs are stout, and dcntated or spinous on the inner 

 side. The Tarsi have but two pellets. The posterior cells of the 

 wings are complete or closed before tiie margin, and narrow or elon- 

 gated, oblique or transverse. 



These Insects compose the genus 



Mydas, 



Which is divided into two subgenera. 



Cephalocera, Lat., 

 Where the proboscis is in the form of a long and projecting siphon *. 



Myoa?, Fah., 

 Ov Mydas proper, Avhere that or an, as is usual in this family, ter- 

 minates by two large lips f . 



In the others, the antenme aie scarcely longer than the head, cylin- 

 drical, 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. 



Chiuomyza, IVied., 



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

 two last of which are the smallest |'. 



Paciiystomus, 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 antennae 

 always composed of three joints, the last of which, the longest, with- 

 out stilet or seta, and divided into eight rings, is clavate in some, 

 and almost cylindrical or in the form of an elongated cone in the 

 others. The wings are usually incumbent on the body. The tarsi 

 are furnished with three pellets. 



These Insects may be united in one generic section. 



Xylophagus. 



In some, the antennae are much longer than the head, with the two 

 first joints very short and the third very long, compressed, forming 



* A subgenus established on an Insect from the Cape. 



f See Fab., Lat., and particularly Dalm., Dipt. Exot., 115, wlio describes seve- 

 ral species. This subgenus and the preceding cue appear to form a particular divi- 

 sion, which, in a natural order, should perhaps be placed higher. The wings have 

 some affinity with those of the Pangonite. 



X Wied., Dipt.. Exot., I, viii. 



§ Lat., Gener. Crust, et Insect., IV, 286 ; Encyc. Method., article Pachi/siome, 

 The larva of the P. s';/rphoule ; Panz., Fauu. Insect. Germ., Ixxvii, 9, the female; 

 lives under the bark oi the Pine ; its pupa resembles that of a Tabanus. 



