290 On Diptera from Vera Cruz. 
raised portions of the tergum are shaded with soft brown, 
only the bases and tips being yellowish. My specimens re- 
mained in alcohol for nearly a year, so that I cannot give a 
more detailed colour description. From memory, however, 
I can say that the soft brown and yellow colours blended so 
as to give a very pretty effect, and I could hardly describe 
the insect as generally pale testaceous or yellow. Both Say 
and Wiedemann, in their descriptions, convey the idea that 
the tergum of abdomen is unicolorous, whereas in the present 
form the colour is well contrasted between soft brown and 
yellow in life, changing to brown and pale yellowish in 
alcoholic specimens. There is also, as ] remember, a creamy 
bloom on the yellow portions in life, which heightens the 
colour effect. The legs are yellowish. The thorax has the 
darker lateral and posterior margins. The specimens vary in 
length from 2 to 4 millim., the usual size being 3 to 33 millim. 
Allowing for brevity in Say’s description, and also for the 
possibly poor condition of his material, it is nevertheless my 
opinion that these Mexican specimens form at least a good 
variety of depressa. 
Twenty-six of the females contain each a black puparium 
within the abdomen, well formed and nearly ready to escape. 
Others show it less advanced. ‘Twenty-one of the specimens 
have a much narrowed form, the abdomen being the same 
width as thorax, and about the same size as latter. This 
form represents individuals that have recently emerged from 
the puparium. It may be noted that in these the lateral 
elytra-like pieces of tergum are not wrinkled or compressed 
to any extent; but the rest of tergum, which in the fully 
developed adult is spatulate and widened behind, is much 
wrinkled and compressed, indicating its recent escape from 
the puparium. 
The puparium is 2 millim. long; 13 millim. wide at widest, 
which is across middle; and 1 millim. thick at thickest, in 
centre as seen from a lateral view. It is polished chestnut- 
brown, with a well-defined yellowish stripe around whole 
edge except at the cephalicend. The cap is shining blackish. 
Whole puparium is shining, rather short oval in dorsal out- 
line, the cephalic end more tapering; slightly flattened or 
less convex on ventral surface, so as not to give a symmetrical 
profile view. 
The abdomen of the male is rounded behind, rather entire 
in outline on posterior edge, hypopygium concealed, genital 
orifice removed a little from posterior edge of ventral surface. 
The abdomen of female is truncate behind, the posterior 
margin rather deeply emarginate on each side of genital 
