MYDAID.E. IgI 



comprises the largest of known diptera. The relation- 

 ships of the family are very close with Rhaphiomidas of 

 the Apioceridae, through the Tricloninae. 



The larvae of species of Mydas live in decaying wood, 

 and it is probable that other members of the family have 

 similar t 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 segments for locomotion; the body 

 is depressed and somewhat widened, with the posterior 

 extremity broader and somewhat obtuse. The pupa of 

 M. clavatus has at its anterior end two strong, sharp, out- 

 wardly curved hooks; the first abdominal segment has 

 at 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 seg- 

 ment; and, on the same segment there is a pair of hooks 

 at the tip curved downward. 



TABLE OF GENERA, 

 i. Terminal segment of the female abdomen with a circlet of spines. 3 

 Terminal segment of female abdomen without circlet of spines. 2 



2. Antennae but little longer than the head, the third short and the 



fourth expanded ; cross-vein between the second and fourth 

 posterior cells present or not (1, 2) . . Dolichogaster. 

 Antennae much longer than the head, the third and fourth joints 

 elongated; the latter moderately or but slightly expanded {P/iy- 

 lomidas)*. (Fig. 1, and 3.) Mydas. 



3. Hind tibiae of female with spur; a short vein ends in hind margin 



of the wing between the second and fourth posterior cells. 



Ectyphus. 



Hind tibiae of female without terminal spur; no such cross-vein; 



proboscis elongate. Leptomydas. 



* I have examined specimens of Phylomidas phylocerus, the type 

 species of the genus, from Norton County, Kansas, in the University 

 of Kansas Museum. The genus is not valid, differing from Mydas 

 only in the more expanded fourth antennal joint. 



