191 



organs usually elevated, one of them much longer than the other in 

 Ptychopteridae, the two normally of equal length and usually slender 

 in Tipulidae, ear-like, appearing like vertical plates, in some Limno- 

 biidae, while in Rhyphidae they are but little elevated and rather stout. 

 Abdomen in Rhyphidae and most Tipulidae circular in cross-section, 

 usually with 2 transverse series of more or less leaf-like or thorn-like 

 protuberances on each segment. 



Imago. — Distinguishable from all other Nematocera by the pres- 

 ence of the discal cell of wing. Mycetobia has no discal cell. This 

 genus has been placed by most writers in the Mycetophiloidea, but 

 lately its affinities with Rhyphidae have been considered closer, and 

 Edwards traces in the presence of a well-defined gular plate a distinct 

 connection with that family, this plate being almost invariably absent 

 in Mycetophilidae, and even when present differing materially from 

 that of Mycetobia. The venation of the Mycetobia wing differs from 

 that of Mycetophilidae in that the second branch of the radius has its 

 base proximad of the radio-medial cross-vein instead of distad of it. 

 The female of Mycetobia has chitinized spermathecae, this character 

 separating it from Mycetophilioidea, no genus of which possesses them. 

 Some Tipulidae have no discal cell, but they all have a distinct 

 V-shaped suture on the dorsum of the thorax — a character which dis- 

 tinguishes them from other Nematocera. Ptychopteridae possesses an 

 incomplete V-shaped or slightly sinuous thoracic suture, and in com- 

 mon with related Nematocera, except Rhyphidae, has very long legs, 

 slender wings, and a long slender body. 



Allocation of species of the families must be arrived at by using 

 the key to families of the Nematocera on a previous page. 



Family TIPULWM 



This family as limited in the present paper contains only three 

 subfamilies : Dolichopezinae, Ctenophorinae, and Tipulinae. Only 

 the two last named are known to me in their immature stages. The 

 number of species of Ctenophorinae in North America is small, but 

 the genus Tipitla, in Tipulinae, contains a very large number of 

 species, the larvae, pupae, and imagines of which in very many 

 cases bear a striking resemblance to each other. With the present 

 collection it is not possible for me to do more than to indicate the 

 principal characters useful in distinguishing the larvae and pupae 

 from each other and from those of other families. 



