SO DIPTERA OF NORTH AMERICA. [PART III. 



and coloring from the preceding abdominal segments. The wings 

 show the complete venation of the Diptera acalyptera ; the 

 auxiliary vein is entirely separated from the first longitudinal 

 vein, although often very much approximated to it ; it runs into 

 the costa at a more or less acute angle, without becoming indis- 

 tinct at its end ; the two posterior, so-called small basal cells, 

 are of a rather considerable size. 



Relationship of the Ortalid^:. 



The great variety of forms occurring among the Ortalidse 

 accounts for the number of their near or distant connections 

 among other families. A relationship of the first degree, which 

 finds its most distinct expression in the similarity of the structure 

 of the male hypopygium and of the female ovipositor, connects 

 them with the Trypetidse and the PallopAeridse, as well as these 

 two families with each other. All three form a very close circle 

 of relationship, the members of which have very similar habits. 



The Ortalidse differ from the Trypetidse in the absence of a 

 second, external row of frontal bristles, and in the course of the 

 auxiliary vein, which, in the Trypetidse, is obliterated at the 

 end and turns rather abruptly, at a more or less right angle, to- 

 wards the costa. 



From the Pallopteridse, the Ortalidse differ in the more con- 

 siderable size of the two posterior basal cells. 



A relationship of the second degree connects the Ortalidse with 

 the Sejosidse and Calobatidse, as well as these families with each 

 other. Both differ from the Ortalidse distinctly in the structure 

 of the male hypopygium and the want of a horny, three-jointed 

 ovipositor, ending in a simple, hairless point. The Sepsidse dif- 

 fer moreover in their rudimentary palpi from the Ortalidse, as 

 well as from the Calobatidse. 



With those of the closely related families which, among their 

 characters, have an erect preapical bristle before the tip of the 

 tibiae, and, at the same time, do not have any vibrissa, that is, 

 with the Sapromyzidse and Sciomyzidse, the Ortalidse have only 

 a very distant relationship. I would have left it unmentioned if 

 the genus JRhopalomera, which I consider as belonging to the 

 Sapromyzidse, had not been placed among the Ortalidse. The 

 presence of an erect bristle before the end of the tibiae, the differ- 

 ent structure of the hypopygium in the male, the absence of an 



