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: Cyclorrhapha.

Family: Muscidse.

Series: Muscidse acalypteratse.

Subfamily: Drosophilinse.

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

Antennse three-jointed, with an arista on the terminal joint; longitudinal v«gins never
branched; "not more than three posterior cells, of which none but the first is jver 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).    Squamse 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 m^atter of convenience. It seems
impossible to get a classification into subfamilies that will be generally
satisfactory. Certain forms obviously belong close together (e. g., in
the present case, Drosophila, Scaptomyza, 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-