34 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
various structural and color characters. For other genera this would 
probably not hold good in all cases. 
As regards Sarcophaga a further tentative suggestion is offered. 
It is not the ambition of the writer to split hairs, but it seems possible 
that this genus, even in the restricted sense treated m this paper, may 
be a more or less heterogeneous group of species, not a natural genus. 
Whether this be so or not, will not be definitely ascertained until a 
larger number of species have been determined and the genus as at 
present recognized has become better known in its cosmopolitan 
relationships. 
The writer had hoped to be able to present the figure of a hypo- 
thetical penis from which those of the various species of Sarcophaga 
might have been derived, but owing to the lack of a sufficient variety 
of material this has been impossible. 
Discussion of Characters. 
The discussion which follows will often include references to other 
genera than the three directly concerned. Unless otherwise expressly 
stated or implied, the term variation as herein used means variations 
of specific value within a genus not differences of an individual charac- 
ter within a species. 
Head. — In profile the head is more or less four-sided and roughly 
trapezoidal. The back of the head, while somewhat convex, is 
slightly flattened and in Sarcophaga hclicis Townsend as well as in 
certain species of Blaesoxipha this is rather pronounced. The front 
protrudes more or less prominently beyond the anterior limits of the 
eyes ; in the descriptions of the species this is expressed by the phrases, 
front very prominent, front prominent, front not prominent (PI. 1, 
fig. 6; PI. 2, figs. 8, 10). 
The color of the parafrontals and genae, as viewed from the front, 
varies from grayish or silvery white, through brassy shades, to golden. 
As a rule it is fairly constant within a given species, but among those 
which have an extended range (Ravinia communis, Sarcophaga hacmor- 
rhoidalis, etc.) variation is apparent. Specimens of a species that are 
taken in the south or in the tropics are apt to be more brightly colored 
than those from farther north. In fact, a golden coloration is rather 
common among tropical and semitropical species, while the less 
intense colors prevail among those of the temperate regions. When 
