241 



The two lots of larvae from which the foregoing description was 

 made, were collected by Dr. Forbes in Yellowstone National Park in 

 1890, one on August 8, in Yellowstone Lake, and the other on August 

 13 in Alum Creek, both collections being obtained among weeds. 



Family RHYPHIDAB 



This family is very small, containing only three genera from 

 North America. One of these, Mycetohia, has been but lately assigned 

 to the family, having previously been regarded as belonging to the 

 Mycetophilidae. According to the differentiating characters previous- 

 ly considered by taxonomists as of family value, Mycetohia appears to 

 belong to Mycetophilidae rather than to Rhyphidae; but the larval 

 and pupal characters unmistakably ally it very closely with Rhyphus. 

 The early stages of Olbiogaster are not known to me. I have before 

 me all stages of Rhyphus punctatus Meigen and Mycetohia divergens 

 Walker, and describe and figure them herewith. 



FAMILY CHARACTERS 



Larz'a. — Very slender, tapering towards extremities. Head com- 

 plete, subcorneal; antennae distinct; mandibles opposed; maxillary 

 palpi poorly developed. Thoracic segments simple, longer than broad, 

 and, like those of abdomen, circular in transverse section ; prothoracic 

 spiracles distinct. Abdominal segments divided transversely as in 

 Therevidae ; pseudopods absent ; apical segment tapered ; spiracles of 

 moderate size, terminal, surrounded by 5 short processes in Rhyphus. 



Pupa. — Slender. Head, between antennae, with 2 slight protuber- 

 ances, each of which is surmounted by a weak hair; antennae curved 

 round in front of and over upper margin of eyes, extending to bases 

 of wings; palpi straight on apical portion and directed laterad. 

 Thoracic respiratory organs but little elevated; fore tarsi overlying 

 mid pair, the latter overlying hind pair, both mid and hind pairs sur- 

 passing apices of wings. Abdomen armed with 2 transverse series of 

 thorns on each segment ; spiracles small but distinct. 



Imago. — The imagines of the three genera are more diverse in 

 structure than are the genera in most families of the Nematocera, and 

 it is possible that some future writer may separate them. A general- 

 ization of the generic characters will be found in the synoptic key to 

 the Nematocera on a previous page. 



