AMERICAN DIPTERA. 199 



well developed and often entirely separated from the second. It has 

 been called the lotver appendage. In the following descriptions the 

 three will be referred to as the first, second and third appendages 

 respectively, or as the upper, middle and lower, where there are three 

 present ; and in the figures they are lettered A, B and C respectively. 

 The varying shapes of the three appendages will be shown in the 

 special descriptions. The second has an almost constant character, 

 however, that may be mentioned here. This is a thickening on the 

 outer side of the anterior edge that appears as a partially detached 

 and reflected plate, and nearly always ends in a free point above 

 lying against the outer surface of the main body of the appendage. 

 Typical examples are figures 88, B; 89, B ; 121, B; and 159, B. 



The tenth segment is a well developed tube, especially in Tipula, 

 with the anus at the end. It arises from the dorsal part of the an- 

 terior wall of the genital chamber. It is generally contained within 

 the latter, but in some cases projects prominently out of it (fig. 149, 

 a. t). In shape it is most often trihedral, one ridge being dorsal, 

 and is always membranous, though in a few cases chitinous plates or 

 bars appear in its walls. 



Genus PACHYRRHIXA Macq. 

 This genus is placed first in the series, because in the external 

 structure of the hypopygium it most nearly resembles Bittacomorpha 

 and PfycJwptera. 



I'achyrrhiiia polyniera Loew (PI. XI, figs. 50, 60). 



The hypopygium forms only a slight enlargement at the end of 

 the abdomen. The eighth tergum is normal, the eighth sternum 

 enlarged and prolonged beneath the ninth. 



The tergum of the hypopygium is a simple convex plate, consid- 

 erably wider than long, the posterior margin deeply cleft mesially, 

 produced into a short outward curved point on each side. The ster- 

 num is a large plate with a double rounded posterior border, being 

 deeply notched mesially. Continuous forward from the apex of the 

 notch is a narrow, median, membranous space reaching almost to 

 the anterior margin of the sclerite. At the anterior end of this 

 membranous area there is raovably attached a short cylindrical ap- 

 pendage projecting downward and posteriorly, and bifid at the tip. 

 Each pleural plate extends the extire length of the hypopygium 

 (fig. 60), but anteriorly it is fused below with the sternum. 



TRANS. AM. ENT. 80C. XXX. JULY. 1904. 



