1924] Concerning the Availability of Taxonomic Characters 167 
CONCERNING THE AVAILABILITY OF CERTAIN TAX- 
ONOMIC CHARACTERS AND THEIR SIGNIFICANCE. 
(DIPTERA).i 
By C. Howard Curran. 
Ottawa, Ontario, Canada. 
During the past year or more I have been engaged at various 
intervals in searching for new characters available in the clas- 
sification of Diptera, and these efforts have resulted, in some 
cases, in the selection of characters which will evidently prove of 
value in due time. Mr. J. R. Malloch has pointed out that the 
Tachinidae are readily separated from the remaining groups of 
the Muscoidea by the presence of a strong convexity beneath 
the scutellum. From an examination of various families I find 
that this development is limited to three of them. I would 
suggest that this portion of the anatomy be termed, for con- 
venience, the “metascutellum.” 
In a paper now in the hands of the printer, I have pointed 
out that I consider the Syrphidse more closely allied to the 
Stratiomyidse than is generally supposed and also their evident 
relationship to the Calyptratse. As the families Stratiomyidae, 
Syrphida) and Tachinida3 (inclusive of the Dexiidse) are the three 
families known to me which possess a metascutellum, considerable 
confirmation of my previous conclusions has been secured. The 
possession of many characters in common by these three families 
would appear to indicate a much closer relationship than has 
heretofore been accorded them by taxonomists. 
It appears that the Tachinidae and Syrphidae are both 
evolved from an ancestor more or less of the Stratiomyid type, 
the three families possibly having a common ancestor. At any 
rate it seems probable that the two first mentioned families 
originated within a reasonably short time of each other from 
common stock or very closely related forms. 
^Contribution from the Division of Systematic Entomology, Entomological 
Branch, Dept, of Agric., Ottawa. 
