AMERICAN DIPTERA. 223 



In harmony with this view the genus Ctenophora, in which all the 

 hypopygial plates are fused, follows Tipida. 



Tipnla fallax Loew (PI. XVI, figs. 133, 135, 137, 138). 



The hypopygium and the three segments preceding it form a large, 

 oval, terminal enlargement of the abdomen, directed upward and pos- 

 teriorly at an angle of about 45 degrees with the much slenderer part 

 in front. The eighth sternum is very large and is produced poste- 

 riorly beneath the hypopygium. It tapers posteriorly to a truncate 

 end where it bears three blunt, conical elevations, one median and 

 two lateral, each of which is covered with a thick growth of short 

 hair. 



The hypopygium is unusually large through being greatly elongate 

 (fig. 138). It resembles in an exaggerated degree the hypopygium 

 of Tipnla truncorum. The sides of the tergum are not fused with 

 the sternum, and converge slightly posteriorly. The posterior mar- 

 gin is rounded. From beneath the margin, however, there projects 

 downward a small, median, chitiuous knob bearing a sharp slender 

 tooth. 



A ventral view of the hypopygium (fig. 135) shows clearly that it 

 is constructed, with modifications, on the same plan as in Tipula 

 bella (fig. 124) and T. mloptera (fig. 129). There is present ante- 

 riorly a large, shield-shaped, membranous area. Back of this area, 

 however, there is a long continuously chitinous space intervening 

 between the membranous area and the posterior notch of the ster- 

 num. This intervening chitinous space is evidently formed by the 

 fusion of the edges of the narrow anterior part of the notch in other 

 species. From its posterior margin there projects backward two 

 long slender sinuous blade-like processes (fig. 135, a), each slightly 

 curved upward at the tip. 



There are no pleural sutures present in this species. The part of 

 each lateral sternal plate corresponding with the pleurum is pro- 

 duced backward in a short, blunt point. Ventrad to this and close 

 to the posterior margin is an oval, membranous feuestrum. From 

 the sternal margin, ventrad to this, there arises a large appendage 

 (figs. 135 and 138, b), consisting of a central body and three arms. 

 One arm extends posteriorly and inward, the second inward, the 

 third, which is much longer than the others, extends anteriorly and 

 inward. 



TRANS. AM. ENT. SOC. XXX. JULY. 1904. 



