ZooL.— Vol. III.] SNODGRASS—DOLICHOPODID HYPOPYGIUM. 279 



where it continues the general course of the anterior part 

 of the sheath. It ends in a large upright bar terminating 

 in a strong point directed forward. The left lobe is narrow 

 and turned dorsally at its base. Beyond this part it expands 

 and turns posteriorly and downward. The posterior edge 

 of the expanded part bears a large flat triangular process 

 projecting backward. The lower end of the lobe rapidly 

 tapers, and then ends in a slightly enlarged part turned 

 again upward and posteriorly. The right wall of the sheath 

 is much higher than the left. 



The penis is rather thick but rod-like. The part within 

 the sheath bears a large plate-like expansion on its left side 

 (figs. 4 and 6). A pectinate lobe (fig. 6) lies against the 

 right side of this plate at its posterior end, just beneath the 

 tubular part of the penis. 



The clasping appendages of the hypopygium are three in 

 number on each side (fig. 5, a, b, and b'). The upper one 

 {a) is hook-like, being wide basally, tapering and bent 

 downward distally. The middle one is wide and triangular. 

 The lowest is slenderer and straight, with a small upturned 

 terminal head. 



The lobes of the tenth segment are short and triangular, 

 and are broadly joined to the median part (fig. i, x). 



Psilopus sipho Say. 



Plate XXXI, Figs. 7 and 9; Plate XXXII, Fig. 2. 



The opening of the ninth segment into the eighth is 

 slightly farther forward on the side of the hypopygium in 

 this species than in most of the other forms examined, and 

 encroaches somewhat upon the anterior surface. The 

 ventral surface of several segments preceding the seventh 

 is deeply grooved for the reception of the upturned hypo- 

 pygium. The seventh segment (fig. 9, vii) is funnel- 

 shaped, the smaller end being anterior. The posterior 

 ventral lobes {d) of the hypopygium are triangular. 



The penis projects a short distance back of the hypopyg- 

 ium (fig. 9, 7^.)' The terminal part is enlarged and the tip 



