ZOOL.— Vol. III.] SNODGRASS—DOLICHOPODID HYPOPYGIUM. 275 



Dolichopus crenatus O. S. 



Plate XXX, Figs. 1-9. 



The pregenital part of the abdomen is ovate in shape 

 (fig. i), broadly joined to the thorax, tapering posteriorly 

 to a point formed of the fifth segment with the sixth mostly 

 retracted within it. The sterna of segments iii to vi 

 form a deep groove between the lower edges of the cor- 

 responding terga, in which is lodged the ventral part of the 

 hypopygium, the latter being ordinarily bent forward 

 and upward upon its peduncle. The fourth sternum is 

 V-shaped with the apex directed forward, the space between 

 the arms being membranous. The fifth sternum is entirely 

 lacking. The sixth consists of a U-shaped bar open pos- 

 teriorly. From the rounded apex of the latter a narrow 

 median bar of chitin runs forward in the membranous roof 

 of the groove to the angle of the fourth sternum. 



The seventh segment forms the peduncle of the hypopyg- 

 ium. It is loosely united to the sixth by a wide flexible 

 membrane (fig. 2), allowing considerable movement be- 

 tween the genital and pregenital parts of the abdomen. 

 The tergum of the seventh segment (/.) is a transverse 

 sclerite having the lateral parts produced downward and 

 posteriorly. The latter meet the anterior part of the small 

 median sternum (5.), which lies entirely posterior to the 

 dorsal part of the tergum, and projects backward beneath 

 the anterior end of the hypopygium and the anterior half 

 of the eighth segment. 



The eighth segment (figs. 2 and 3, viii) forms a flat 

 scale-like plate, roughly triangular in outline, lying upon 

 the anterior part of the left side of the hypopygium. Its 

 form, as seen from the right, is shown in figure 7. It is 

 evident that its true right side is reduced to the narrow 

 vertical bar lying opposite the anterior edge of the leftside. 

 The posterior foramen is lateral, lying back of this bar, 

 and occupying nearly all of the actual right side of the seg- 

 ment. The anterior foramen is a narrow vertical opening 



