340 Professor Aldrich on the 



yellow ; antennae pure yellow, with long brownish arista ; cilia of 

 inferior orbit yellow. Thorax shining green, somewhat bluish, 

 decidedly globose above on the anterior part. Scutellum short 

 and wide, crescent-shaped, with one pair of bristles (the outer pair 

 are microscopic). Pleurae black, the posterior margin, tegulge, and 

 halteres light yellow ; cilia of tegulse yellow. Abdomen shining 

 bluish green, the venter yellow, sixth segment wholly yellow. 

 First joint of hypopygium yellow, small, lying along the basal 

 and dorsal (outer) surface of the second ; the latter brown, 

 elongated, tapering, at its apex with a pair of minute, delicate 

 yellow lamellae, fringed with light yellow hairs. The interior 

 organs, arising from the basal portion, are three in number — a 

 long, straight, sharp, yellow central one (penis ?), and two slender 

 biire yellow filaments ; the former is about as long as the hypopy- 

 gium itself, the latter are much longer, somewhat crooked in the 

 described specimen. Coxae and all the legs pure light yellow, 

 almost destitute of bristles. Wings hyaline, the veins yellow. 



$ . Somewhat smaller, otherwise not materially different. 



Length 1"2-1*5 mm. 



One male, numerous females. May, March. Two 

 other males, more shrivelled and discoloured, are con- 

 siderably darker than the perfect specimen here 

 described. 



2. Xanthotricha minor j n. sp. 



Resembles the preceding, except in the following respects : 

 The general colour is somewhat darker, the venter and sixth seg- 

 ment not yellow, male hypopygium blackish, the delicate parts 

 shrunken and difficult to make out, but apparently without the 

 long filaments so characteristic of the preceding ; pleurae wholly 

 bluish black ; the posterior cross-vein is shorter, in consequence of 

 the fact that the fourth vein bends back to meet it, forming a 

 distinct angle at this point. The last character is sufficient to 

 separate the two species. Length 1*2 mm. 



One male, two females. 500 feet. 



3. Xanthotricha singularis, n. sp. 



Still a third species of this minute genus differs from the first 

 in its extremely small size, in its colour, which is in general the 

 same as the second, and in the singular structure of the male 

 hypopygium. This bears a close resemblance to the ovipositor of 

 a female, extended to its full length and bent under the abdomen. 

 Only by using a power of several hundred diameters could I 



