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PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 78 



Wings hyaline, third vein with three bristles at base and the costal 

 spine short, scarcely discernible. 



In his original description, Williston merely cites the characters 

 which he considered differentiated the species from archippivora. 

 Of the latter species his description of the abdomen reads as follows : 

 "Abdomen black, short, thickly gray pollinose, variable in different 

 reflections; second segment with a posterior pair of bristles, no 

 median bristles on this and the next segment; the general covering 

 of short bristles well differentiated from the long bristles." 



The description that follows is of a male from Massachusetts bred 

 from the same host as was Williston's species, compared with his 

 type and regarded as typical. First segment black, subshining 

 except at venter where it is thinly gray pollinose ; second and third 



segments black, subshin- 

 ing, the dorsum and venter 

 thinly gray pollinose, va- 

 riable in different reflec- 

 tions but noticeably thicker 

 at the bases, apices shining 

 black both dorsally and 

 ventrally; fourth segment 

 black, gray pollinose, the 

 tip black, subshining. First 

 segment with one pair of 

 median marginal bristles; 

 second with a median mar- 

 ginal and lateral pair; 

 third with a marginal row, 

 the bristles of which are equal in length to dorsum of fourth seg- 

 ment; fourth wholly covered with bristles, the marginal and sub- 

 marginal rows being much the strongest. 



Genitalia (figs. 1, 2) small, black, shining on sides, the dorsum 

 without luster; forceps viewed from behind, at greatest width over 

 one-half their length. Inner forceps shining black, fused for about 

 one-half way, with the basal portions separated by a well defined 

 keel. Viewed in profile, the inner forceps are slightly convex and 

 terminate in blunt points, their length scarcely one-half the length 

 of the fourth abdominal segment; outer forceps black or reddish, 

 moderately broad at base and tapering slightly to rounded points. 

 Length, 6-7 mm. 



The type is deposited in the Museum of Comparative Zoology, 

 Cambridge, Mass. 



The species is a decidedly complex one with a wide range and 

 probably includes several undescribed forms which are at this mo- 



FlGDRES 1 AND 2. ACHAETOXBURA FEENCHII 



(Williston), male genitalia, l, from be- 

 hind ; 2, SIDE VIEW 



