278 BENJAMIN P. YouNG 
species sometimes give one the impression that the epimeron of the meta- 
thorax is an abdominal sclerite and the first tergite is a thoracic sclerite. 
Because, for the most part, this confused condition exists among the 
Brachycera, attention is called to it. This is the case in all the families 
except the Stratiomyiidae (Plate XV, 19), the Empididae (Plate, XVIII, 
30), the Lonchopteridae (Plate XTX, 31), and the Phoridae (Plate XIX, 32). 
Perhaps one of the clearest characters that nature has supplied in the 
area studied, and one on which the whole group of flies can be divided, 
is the pleural suture of the mesothorax. In the Nemocera with the excep- 
tion of the Psychodidae, and in the Brachycera with the exception of 
the Cyrtidae, this suture runs more or less straight from the coxa to 
the wing process. If it bends forward at all it is on a rather easy curve, 
but in all the Brachycera of the Orthorrhapha, with the exception of the 
one cited above, and in all the Cyclorrhapha, this suture takes an abrupt 
turn cephalad (in some cases the angle is equal to 90° or more) in its course 
from the leg to the wing area. 
Lastly, the writer wishes to call attention to the presence of a tongue- 
like structure in the membrane of the mesothoraciec coxae of all the 
Calyptratae and the Acalyptratae, with the exception of the Oestridae, 
and its absence in all other families except the Syrphidae. 
These characteristics do not as a whole point to the same places for 
the division of the order as the one adopted in this paper, or to any other 
single classification. But there are characters, such as the presence or 
absence of the adventitious suture and the character of the pleural suture 
of the mesothorax, which divide rather definitely where they strike and 
‘should be of value for that reason.- Certainly this investigation has 
emphasized the fact that the last word has not been said on the systematic 
position of some members in such families as the Cyrtidae, the Oestridae, 
the Scatophagidae, the Ephydridae, the Oscinidae, and a number of others 
whose study has offered obstructions to uniformities within a time-honored 
system. 
