62 NORTH AMERICAN DIPTERA. 



TABLE OF GENERA. 



1. Proboscis short, protruding but little from the oral opening; eyes bare 

 or pilose; two or three submarginal cells. HIRMONEUBA Meigen. 



Proboscis long, directed backwards ; antennae broadly separated ; eyes 

 bare; ovipositor of the 9 composed of two slender lamellae; three 

 submarginal cells present. . . RHYNCHOCKPHALUS Fischer. 



20. MYDAID^E. 



Rather large to very large, thinly clothed or bare, elongate 

 flies. Neuration complicated, the basal cells long ; the fourth 

 vein always terminating at or before the tip of the wing. 

 Antennse elongate, the third joint flattened, with a terminal 

 lamella. Front excavated between the eyes. Ocelli wanting. 

 Proboscis short, with fleshy labella and without palpi (in our 

 species). Empodia very little developed, not pulvilliform. 



The family Mydaidse comprises only about one hundred 

 known species, but among them are the largest of the order, 

 a few measuring two inches in length and rivaled only by the 

 Acanthomeridae among the other families of diptera. The 

 larvae of species of Mydas live in decaying wood, and it is 

 probable that all the members of the family have similar 

 habits. They are known to be predaceous in some cases upon 

 the larvae of beetles. The larvae of M. fulvipes are nearly 

 two inches in length, with swellings below the abdominal seg- 

 ments for locomotion ; the body is depressed and somewhat 

 widened, with the posterior extremity broader and obtuse. 

 The pupa of M. clavatus has as its anterior end two strong, 

 sharp, outwardly curved hooks ; the first abdominal segment 

 has, on its anterior border above, a row of very long, erect 

 spines curved backward at the tip. Another series of spines 

 is situated on the anterior border of the last segment, and, on 

 the same segment there is a pair of hooks at the tip curved 

 downward. 



