June,1919 Bulletin of the Brooklyn Entomological Society 111 
THE LIMITS OF THE DIPTEROUS GROUP CALYPTRATA 
(CYCLORRHAPHA). 
By J. R. MAttocn, Urbana, Ill. 
In connection with some work I have been doing on cyclor- 
rhaphous Diptera I have been forced to decide upon characters 
which will enable students to separate the calyptrate and acalyp- 
trate forms with more certainty, less trouble and experience, and 
a nearer approach to a natural arrangement than is possible by 
using any existing textbook. Practically all the writers who at- 
tempt to deal with the matter base their separation of the groups 
upon the comparative size of the calyptra, the calyptrata being 
said to have large calyptra while the acalyptrata have these or- 
gans very small or absent. In the case of the Tachinide and the 
other highly specialized forms the very large calyptra readily dis- 
tinguish these insects, but many of the genera in Anthomyiide 
and especially in Scatophagidz have the calyptra very small and 
such forms cannot be distinguished from acalyptrates by the size 
of these organs. It is thus impossible to use this character for 
distinguishing the two groups, and as a matter of fact in practice 
it either misleads the student or leaves him in doubt as to which 
group his species belongs to. Some recent writers have tried to 
make clearer, by elaboration, the distinguishing characteristics of 
the groups, but as all of them have persisted in placing the Scato- 
phagidz in the acalyptrates such attempts have been invariably 
unsuccessful. 
It is my opinion that in order to be appropriately applicable to 
groups of the status of these two in all cases the differentiating 
medtum should consist of one or very few characters which 
should be, not of a comparative nature, but more or less inti- 
mately associated with the biological characteristics of the groups 
and in a definite manner indicate evolutionary relationships— 
1. e., the character (structure, usually external) should be one 
which is either present or absent, or the position of which differs 
strikingly in the two groups. 
In other- words the character or characters should clearly in- 
dicate natural affinities, be readily appreciable even to students 
