I5 6 NORTH AMERICAN DIPTKRA. 



tains a number of species of wide distribution. The 

 genus Olbiogaster is known from two or three species 

 hitherto recorded only from Mexico and the West Indies. 

 ' It differs from Rhyphus in the structure of the head (eyes 

 separated by a broad front in both sexes, and occiput but 

 very little developed), of the antennae (scapus short, fla- 

 gellum of male filiform, etc.), of the thorax and abdo- 

 men, as also in the venation.' (Osten Sacken.) 



The larvae of Rhyphus are worm-like, legless, naked, 

 more or less transparent, with snake-like movements; 

 there are two, short, fleshy points at the posterior end. 

 The pupae are free, inactive, with two projections ante- 

 riorly; they live in water of brooks, pools or puddles, or 

 in rotting wood, hollow 7 trees, or manure. 



