48 THE NORTH AMERICAN SPECIES OF DROSOPHILA. 



X. SYSTEMATIC ACCOUNT. 



SYSTEMATIC POSITION OF THE DROSOPHILINE FLIES. 



The following represents the classification now current among most 

 students of the Diptera: 



Class: Insecta. 



Order: Diptera. 



Suborder : Cy'clorrhapha. 



Family: Muscidse. 



Series: Muscidse acalypteratse. 



Subfamily : Drosophilinae. 



Muscidae (= Eumyiidae, Myodaria, Oligoneura, Muscoidea, etc.). 



Antennae three-jointed, with an arista on the terminal joint; longitudinal veins never 

 branched; not more than three posterior cells, of which none but the first is ever closed 

 or narrowed at the wing margin; marginal and submarginal cells open; bristles present; 

 empodia never large. 



The family is easily split into two main groups, as follows : 



1. Calypterse (Schizometopa) . SquamsB large; front of male narrowed or 



eyes meeting in front; transverse suture of mesonotum complete. 



2. Acalypterse (Holometopa) . Squamse small; front of male rarely nar- 



rowed, eyes never meeting in front; transverse suture of meso- 

 notum never complete. 



Further subdivision, especially of the Acalypterse, is very difficult. 

 A number of groups (about 20 to 26 generally recognized) have been 

 segregated as subfamilies, or families if the Muscidse are treated as a 

 superfamily. The exact definition of these groups is scarcely possible, 

 as in so many cases there are forms that agree with one group in most 

 of their characters, but are aberrant in other respects. Many keys 

 are to be found, but none, I think, will bring all the forms to the 

 groups where they are commonly placed. There are, scattered all 

 through the Acalypterse, many genera of doubtful affinities. These 

 are put in different subfamilies by each new student. Such forms in 

 the neighborhood of the Drosophilinse are Curtonotum, Apsinota, 

 Aulacigaster, Paratissa, Stenomicra, Periscelis, Amphoroneura, and 

 the forms near Asteia. In the present treatment the three first-named 

 have been included in the subfamily, and the others have been excluded. 

 This has been done largely as a matter of convenience. It seems 

 impossible to get a classification into subfamilies that will be generally 

 satisfactory. Certain forms obviousl}" belong close together (e. g., in 

 the present case, Drosophila, Scapiomyza, Chymomyza, Cladochceta, 

 Mycodrosophila, Leucophenga, Pseudophortica, Zaprionus, Zygothrica, 

 Camilla, and Stegana). Others are more or less like these, and may 

 be included in the group or not, according to the personal equation 

 of the individual student. I have excluded Paratissa because it seems 

 to me more like the Ephydrinse; and Asteia, Crepidohamma, Echid- 



