CLASSIFICATION OF DIPTERA. 19 
The Wemocera anomala are characterized by the following distinc- 
tive features : 
i. Head holoptic, both in the male and female, but chiefly in 
the former. In £7d70, for instance, the ? has non-holoptic 
eyes. 
i. Eyes often bisected, the upper facets being the larger. These 
two halves may be separated by a smooth, unfacetted stripe, 
as in the ¢ -Bidbio. 
iii. Legs well adapted for walking, and often, as in A7dio and 
Simulium, thick. 
iv. Male and female generally differ very much. 
v. Peculiar, often sporadic geographical distribution. 
— 
Upon these characters Osten-Sacken has founded the two divisions 
of the Nemocera. Both from these characters, their curious distri- 
bution, and their archaic nature, we see that this division is quite a 
natural one, and is founded on more scientific principles than most 
entomological classifications. Amongst the Orthorrapha Brachycera 
he classifies the following families into one group: the Zabanide, 
Strationyide, Acanthomeride, Leptide (plus Xylophagide). For a 
long time these families have been converging towards one another, 
and at last have been united under the name (given by him) Zvemo- 
cheta. ‘This seems a natural group, and is founded on a chetotactic 
character ; namely, the total absence of Macrocheteze. 
Besides the bristleless nature of these forms, they are separated 
from the JVemocera and remaining Brachycera by the following 
characters, given by Osten-Sacken : 
1. The eyes in the male are predominantly holoptic. There 
are, however, a few exceptions to this rule given by him ; 
viz., Xylophagus, some Australian Chiromyze, Hermetia, 
etc. But Cenomyia, a close relation to Xylophagus, has 
holoptic eyes. 
2. The variegated colour of the eyes, especially seen in S¢ratio- 
myide and Tabanide. 
3. The extreme variability of the antenne, on the one hand 
related closely to the Memocera, and on the other to the 
Cyclorrhapha. 
4. Three well-developed pulvilli are generally present. Legs 
smooth, and having no bristles, as seen in the Asé/ide, 
Bombylidea, etc. 
The following, then, are the families recently grouped by Osten- 
Sacken : 
2—2 
