16 DIPTERA OP NORTH AMERICA. 



Loew, RACHICERUS Hal, COENOMYIA Latr., and ARTHROPEAS 

 Loew. The new genera CYCLOTELUS, PHYCUS, and DIMASSUS, es- 

 tablished by Walker as belonging to the Xylopkagidee, belong in 

 fact to the Therevidce; likewise NONACRIS must be removed here, 

 but Walker's observations on its characters are far too superficial 

 to admit of any certainty in fixing its place ; also DIALYSIS on ac- 

 count of the hairy, bristle-like antennal tip ascribed to it by Walker 

 might seem to be erroneously located among the Xylophagidce, the 

 characters of which he appears not to have understood. 



Gcenomyia Latr. has often been separated from the Xylophayidce 

 and considered as forming a distinct family : Ccenomyidce, or for- 

 merly Sicarii. This seems to have been caused by the body of 

 Ccenomyia being stout, whereas that of Xylophagus and Sulula is 

 of a slender form. Moreover, the different form of the palpi, which 

 in Gcenomyia are rather cylindrical and ending in Xylophagus and 

 Subula in a button-shaped thickening, have been made use of to 

 justify the separation. But within a recent time forms of Cceno- 

 myidce have been discovered in which the structure of the body 

 and palpi is such as to form a link between them and the Xylopha- 

 gidce; from this, as well as from the agreement of their other 

 essential characters, results the necessity of reuniting them. In 

 case the separation should be maintained, Arthropeas ought to be 

 placed among the Ccenomyidce. 



The family of Xylophagidce may be divided into three sections : 

 CCENOMYINA, RACHICERINA, and XYLOPHAGINA. The Ccenomyina 

 are characterized by their robust structure, the third joint of the 

 antennas being annulated and pointed towards its end, the palpi 

 being cylindrical. The genera comprised here are COGNOMYIA and 

 ARTHROPEAS. In the Rachicerina the third joint of the antenna 

 is divided into separate and frequently very numerous articula- 

 tions, and the palpi are rather club-like ; the body is less heavy 

 than in the Ccenomyina, but less slender than in the Xylophagina. 

 The genera ELECTRA, CHRYSOTHEMIS, and KACHICERUS belong 

 here. The Xylophagina have the slenderest bodies ; the third joint 

 of the antennas is annulated and never strikingly pointed ; the 

 palpi have at their end a button-shaped thickening. The genera 

 SUBULA, XYLOPHAGUS, and PACHYSTOMUS may be referred here. 



I am acquainted with N. A. species belonging to the genera 

 COSNOMYIA, ARTHROPEAS, RACHICERUS, SUBULA, and XYLOPHAGUS. 



