6 AMERICAN DIPTERA. 



membraneous, arising separately from each 'side of tiie venter, curv- 

 ing towards each other, provided, at their apices, with hooks, or, as 

 in alesia Walk., with knob-like swellings, bent over to serve as 

 hooks. These clasps are to lay hold of the ovipositor (as it is here 

 called), the hooks following into a groove which exists beneath the 

 same. The genital segment of female, or ovipositor, is also, as will 

 be seen (in Figure 4), very much enlarged, of irregular shape, not 

 awl shaped as is general with these members; and are not capable 

 of folding under against the venter. These characters alone are of 

 sufficient value for genei'ic separation when compared with those of 

 the other group (Figures 7 and 8). 



This is the common eastern North American species of this group, 

 and may be found upon low herbage in cool shady situations. 



Calobata alej*ia Walker, List, iv, 1048, 1849. (PI. I, fi.es. 5 aud 6.) 



Sbiuing black, with yellow legs. Front in the middle, the vertex and upper 

 median part of the occiput, o])aque; a narrow silvery stripe on each side of ver- 

 tex, running from the inner vertical bristle to the vertical orbit, then on down 

 the frontal orbits to the face; no post verticals, but sometimes two or three 

 minute frontal bristles. Face light yellow; clypeus inconspicuous. Occiput 

 much swollen and whitish pollinose below. Proboscis brown. Antenna; darker 

 than face; third joint slightly longer than the second; arista black, minutely 

 plumose. Thorax with a narrow lateral pollinose stripe fiom the humerus to the 

 scutellum; the lower part of pleura also whitish pollinose; between the fore 

 coxse yellow. Halteres nearly white. Abdomen of male with third segment 

 swollen laterally, then constricting to the narrower fifth ; the genital segments 

 similar to those oi univitta Walk. ; the clasps are much more enlarged than those 

 of the latter species, their apices with pad-like hooks; between these clasps pro- 

 jects a short double knobbed process which are, as are also the clasps, a translu- 

 cent yellow. The abdomen of female is cylindrical ; the ovipositor is also black, 

 of an irregular shape, being wider than the abdomen, with a cordate base, and 

 tapering slightly to a truncate triangular apex. Hind tibije and a band near 

 the apex of hind femora black or brown. Wings hyaline; veins yellow toward 

 the costa; first posterior cell open ; anal cell short. Length 6 mm. 



Both sexes. New Jersey and northern Illinois. 



The drawings will readily show where this species differs in 

 regards to the genitalia, and the synoptic table will give other 

 differences. 



Calobaia aiileiiimpp«'S Say, Journ. Acad. Sci. Phila., iii, 07, 1823. 

 (PI. I. figs. 7 and 8; II, fig. 9.) 

 Brown to black, with yellow markings. Front black; sides shining ; median 

 vitta oiJaque, with whitish reflection ; three or four jtairs of frontal bristles. Ver- 

 tex much wider than front, not diflerentiatcd from, but is rounded into, the 

 occiput; the ocellar tubercle is situated about midway between the post verticals 



