AMERICAiN DIPTERA. l87 



panded laterally near the base, taperill^■ toward each extremity, 

 ending distally in two deflexed points. The penis is a narrow 

 chitinous tube lying in the groove of the gnard, and arising from 

 two diverging roots in front of it. 



The second gonapophyses (fig. -0, gon. 2) consist of two slender 

 ti'iangular plates projecting into the geninal chamber al)ove the 

 guard of the penis, and arising from two long roots that run for- 

 ward to the base of the guard. Tliese really arise from a more dor- 

 sal level than the base of the guard, although not clearly so shown 

 in fig. "20, which is a ventral view of the parts. 



The forms that follow the genera so far descrilied, in the structure 

 of the hypopygium, have the pleural plates excluded from the lat- 

 eral parts of the segment and attached as appendages on its poste- 

 rior rim. The series thus derived from AntocJia and the Limnobina 

 are the genera of the Limnobina Anomala exclusive o^ Antoehu, the 

 Eriopterina, the Limnophilina, the Anisomerina and the Amalo- 

 pina. The genera of the Ptychopterina {BiUacomorpha and Ftij- 

 choptera) constitute another group in which the pleura intervene 

 between the tergum and sternum. From them are derived the 

 genera of the Tipulina, with Pachyrrhin.a as a transitional genus, 

 in which the pleura retreat from the anterior margin of the segment 

 but become fused with the sternum. 



Geuera RHAMPHIDIA Meigeii, uud DICRANOPT Yl'HA O. S. 



In both of these genera of the Limnobina Anomala the hypopy- 

 gium consists of a circular ring-like body, composed of the tergum 

 and sternum, and »f two large lobes attached laterally to the poste- 

 rior rim of this ring. These appendicular lobes are apparently the 

 pleura, for in these genera, and in all the others related to them, 

 they bear distally the apical appendages. 



Genera ERKH'TERA Meigeii. TRIiVIICRA O. S. and 

 SYMPL.E€TA Meigen. 

 These genera represent Osten Sacken's Section III, the Eriopte- 

 rina. They resemble the last two in that the l)()dy of the hypopy- 

 gium is ring like, and the pleura are a})pendicular. 



Erioptera septentriouis O. S. 



The body of the hypopygium consists of a simple ring in which 

 there is not even a suture between the tergum and sternum. The 



TRANS. AM. KNT. SOC. XXX. JULY. 1904. 



