222 R. E. SNODGRASS. 



The penis is unusually thick. In the ordinary condition it lies 

 entirely within the genital chamber and reaches forward to the sec- 

 ond abdominal segment. Figure 72 represents a specimen with the 

 penis partly protruded. In this condition the anterior part of the 

 bend lies in the fourth segment. The central vesicle is correspond- 

 ingly small. The guard of the penis is a triangular plate (fig. 75), 

 with two small lobes arising from its basal angles and converging 

 above its base. With the base of the guard they form a collar like 

 ring which surrounds the penis. 



The anal tube is short, simple and strongly compressed. 



Tipula spernax O. S. (PI. XII, fig. 68). 



The hypopygium has a simple form. The tergum and sternum 

 are united. The latter is deeply cleft below by a narrow, median, 

 seam-like, membranous line. There is a trace of a pleural suture 

 present. On each side a line curves outward and upward from the 

 notch in the sternum below and in front of the part corresponding 

 with the pleurum of Group II. It has rather the appearance of a 

 disappearing suture in this group, than of the suture characterizing 

 Group I. 



There are three apical appendages on each side (fig. 68). The 

 first (A) is a wide, plain lobe, slightly convex outwardly and con- 

 cave inwardly. The second (B) is wide at the base, rapidly taper- 

 ing distally into a slender arm directed anteriorly. The third (C) 

 has a large triangular base lying against the outer side of the base 

 of the second. Distally it tapers into a slender arm abruptly bent 

 forward. 



Group III. 

 Neither pleural sutures nor pleural plates present. 



It is conceivable that this may be a composite group. The lack 

 of any pleural demarkation might be due either to the entire sup- 

 pression of the pleural sutures of Group I, or to the obliteration of 

 the sutures in front of the pleural plates of Group II. The species 

 that fall into this division, however, are not primitive in other char- 

 acters. For example, in several the entire hypopygial wall consists 

 of one continuous plate. There are not only no separate pleural 

 plates, but the tergum and sternum are fused. Hence, the species 

 having the characters of this group are here placed together as rep- 

 resenting the final evolution of the hypopygium in the genus Tipula. 



