228 R. E. SNODGRASS. 



SUMMARY. 



If we assume that the primitive Tipulid hypopygium consisted of 

 a tergum above, a sternum below, and of a pleural plate on each 

 side intervening along the whole length of the segment between the 

 tergum and the sternum, then we must adopt the phylogenetic out- 

 line followed in this paper. Briefly summarized this is as follows : 

 There are two groups of species that present a primitive arrange- 

 ment of the hypopygial sclerites. The first consists of the genus 

 Antoeha and of the section Limnobina. The second consists of the 

 section Ptychopterina which includes Bittacomorpha and Ptychop 

 tera. All of these forms have the pleura in the typical position just 

 described. From the first group have been derived a series of forms 

 consisting of the Limnobina Anomala, except Antoeha (but includ- 

 ing Rhamphidia and DicraJioptycha), the Eriopterina (Trimicra, 

 Symplecta, Erioptera), the Limnophilina (Limnophila, Epiphragma), 

 the Anisomerina (Eriocera), and the Amalopina (Amalopis). In 

 this series the pleura have retracted from the anterior margin of the 

 segment and have become exserted upon the posterior margin, ap- 

 pearing in most cases as appendages on the rim of the genital cham- 

 ber. In Antoeha and in the Limnobina (Dicranomyia, Limnobia) 

 the apical appendages are born by the pleura, but, since these plates 

 are here lateral, the appendages are on the hypopygial margin. In 

 the forms with exserted pleura the apical appendages are, of course, 

 born at the ends of the appendicular pleural lobes. 



From the second primitively constructed group, represented by 

 the Ptychopterina (which includes Bittacomorpha and Ptychoptera), 

 is derivable the series formed by the Tipulina (Pachyrrhina, Tipula, 

 Ctenophora). In some species of Pachyrrhina the pleura closely 

 resemble the pleura in Ptychoptera, since they occupy the entire 

 length of the side of the hypopygium. In most species of the genus, 

 however, the anterior part of the suture between the pleurum and 

 the sternum is obliterated. In many species its anterior end is bent 

 upward for a very short distance at about the middle of the segment. 



The lower members of Tipula resemble the higher forms of 

 Pachyrrhina. in having this "pleural suture" extending about half 

 way to the anterior margin of the segment, and abruptly bent dor- 

 sail v in a small terminal hook-like curve. In the majority of the 



