274 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



slender. It curves forward and downward over the ante- 

 rior wall of the chamber and then goes straight posteriorly 

 a varying distance, extending to or beyond the posterior 

 end of the hypopygium. Its lower part is generally 

 guarded by a semicylindrical sheath arising from the lower 

 part of the anterior wall of the genital chamber. From 

 the posterior edges of the side walls of the latter there 

 arise two pairs of hook-like clasping lobes. The body 

 cavity in the hypopygium opens into that of the eighth seg- 

 ment, not by a foramen at its anterior end, but by an aper- 

 ture situated on the anterior -part of the left side. This is 

 the distinctive character of the Dolichopodid hypopygium. 



The eighth segment itself is small and scale-like, cover- 

 ing the lateral foramen of the ninth, and not extending 

 beyond the anterior end of the latter. Its interior com- 

 municates with that of the seventh segment through a 

 narrow vertical opening at its anterior end. 



The seventh segment forms the peduncle of the hypopyg- 

 ium, being connected with it through the intervention of 

 the eighth segment. Since the latter lies on the left side of 

 the median Hne, the axis of the seventh segment is oblique. 



The sixth segment is small, and usually not much modi- 

 fied, except that its tergum is larger than its sternum. 



The pregenital part of the abdomen, i. e., that part con- 

 taining the principal abdominal viscera, consists of the first 

 to the sixth segments inclusive. The sixth segment is gen- 

 erally retracted partly into the fifth. The hypopygium 

 may be partly or entirely hidden in a groove on the ventral 

 side of the segments before the seventh. 



The tenth segment consists of a small median conical 

 part placed at the upper posterior angle of the hypopygium, 

 and of two large lateral lobes. The latter may be either 

 wide and oval, or elongate and tapering. 



The following detailed description of the abdomen of 

 DoUchofus crenatus may serve as a type for the entire fam- 

 ily. Descriptions of other forms are more briefly given 

 beyond. 



