OF PHILADELPHIA. bi 



tarsal joints black ; tergum paler than the thorax, posterior mar- 

 srins of the seg-nients with a definite black band. 



Length to the tip of the wings seven-twentieths of an inch. 



Very common on the Missouri ; I observed it particularly 

 above Cow Island. 



[The genus is called Helomyza Fall. — Sacken.] 



OLFERSIA Leach. 



0. ALBIPENNIS. — Blackish-brown; wings whitish. [102] 

 > Inhabits Ardea lierodias. 



Mentum white ; thorax with the cruciate lines distinct, the 

 longitudinal line tinged with yellow, humeral tubercle jirominent, 

 pale, obtuse; scutel with an impressed line; nervures brown, 

 inner cellule less than half as long as the preceding one which ex- 

 tends to the base of the wing; pectus with a prominent angle 

 each side between the anterior pairs of feet ; tergum pale brown- 

 ish, with a black base, disk and tip. 



Length one-fifth of an inch. 



ORNITHOMYIA Latr. Leach. 



1. 0. NEBULOSA. — Head yellow ; feet pale ; tibia with two 

 reddish-brown lines. 



Inhabits Strix nehulosa. 



Eyes blackish-brown ; vagina and hypostoma pale ; thorax 

 reddish-brown, with a large yellowish humeral spot and three 

 longitudinal lines, of which the intermediate one includes an 

 impressed line, which interrupts a transverse impressed line ; 

 humeral angle prominent, subacute ; spiracle white ; marginal 

 nervures blackish-brown, those of the disk brown ; scutel red- 

 dish-brown, varied with yellow at base; pectus yellow-white, an- 

 terior margin bifurcated; tarsi dark reddish-brown, nails black; 

 abdomen pale-brownish, with black hair, first segment on its an- 

 terior face pale-yellow. 



Length three-tenths of an inch. [103] 



2. 0. PALLIDA. — Pale; intermediate cellule of the wing ex- 

 tending nearly to the tip of the outer cellule. 



Inhabits Sylvia sialic. 



Eyes blackish-chestnut ; antennae chestnut, tip white ; labrum 

 bifurcated, white ; hypostoma whitish ; front yellow-white, a 

 1823.] 



