DIPTERA. 455 



is usually very short, is almost entirely retracted within the oral cavity. The 

 membranous nature of that organ and its turned up lips, its similarly raised and 

 clavate palpi, the relative disposition of the wings which are usually crossed, 

 the form of the abdomen which is rather oval or orbicular than triangular, and 

 finally the scutellum, which is frequently armed with teeth or spines, also 

 distinguish the Notacantha from the Tabanides. 



But few of their larvae have been observed. Such as have been discovered 

 are described and figured by Swammerdam, Reaumur and Rcesel, are aquatic, 

 and approximate to those of the Athericera in their soft head, varying in form, 

 and in their habit of becoming pupa? under their own skin; but they retain 

 their primitive form and proportions, thus differing from those of the latter. 



Other larva; of the Notacantha Xylophagusli\e in the carious and 

 diseased parts of trees. 



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 antennae, 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 subulate 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 antennae 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. CEPHALOCERA, Lat., where the 

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

 Mydas proper, where that organ, as is usual in this family, terminates by two 

 large lips. 



In the others, the antennae are scarcely longer than the head, cylindrical 

 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, Wiedemann, 



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

 which are the smallest. 



