194 R. E. SNODGRASS. 



inous part of the sternum is deeply cleft in the median line poste- 

 riorly, but the notch is occupied by membrane. The pleura are 

 fused with the lateral parts of the sternum, but each stands out as a 

 prominent triangular lobe on the posterior rim of the hypopygium. 

 Each carries, articulated to it, a long, slender, tapering process end- 

 ing in a recurved hook. 



The penis and its guard have a most unusual form. The two 

 together appear to constitute one structure composed of a short, 

 thick body bearing three terminal prongs projecting posteriorly and 

 a short spike like process projecting dorsally. Above it are two 

 elongate plates lying against the roof of the genital chamber. 



Genera BITTACOMORPHA Westw., and PTYCHOPTEKA Meig. 

 In these two genera we go back again to the primitive structure 

 of the hypopygium found in Antocha and in the Limnobina Ano- 

 mala, where the pleural plates occur in their normal position on the 

 sides of the segment between the tergum and the sternum. Hence, 

 we have two groups of genera possessing this primitive hypopygial 

 structure. From the first we can derive the series of genera, begin- 

 ning with Rliamphidia and ending with Amalopis, in which the 

 pleura are appendicular. From the second group, Section VIII of 

 Osten Sacken, the Ptychopterina, we can derive the genera of the 

 Tipulina, where the pleura again recede from the front of the seg- 

 ment but become fused with the sternum. 



Bittacomorpha clavipes Fab. (PI. X, figs. 35, 36, 37, 38, 39). 



The appearance of the hypopygium in side view is shown in figure 

 35. The eighth segment is here removed and the intersegmental 

 membrane (m.) between the eighth segment and the ninth is exposed. 



The tergum is a large, wide, strongly convex plate, covering not 

 only the dorsal surface of the hypopygium but also the dorsal half 

 of each lateral surface. The posterior margin is concave above (fig. 

 37), convex on the sides. Just above each lower posterior angle 

 there is movably articulated to the posterior margin a long slender 

 appendage extending posteriorly and slightly curved inward (figs. 

 35 and 37, a). These appendages are simply special organs in the 

 species, having no recurving homologous representatives elsewhere. 

 .Similar lobes occur also in scattered cases on the sternum, as for ex- 

 ample, in Ptyehoptera lenis. The notch on the posterior margin of 

 the tergum is occupied by a narrow fold of membrane in which 

 there is situated a small nodule of chitin. 



