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



Hydrophorus algens Wheeler. 

 Plate XXXIII, Figs. 2 and 7. 



In this species all the segments of the genital part of the 

 abdomen are concealed within the posterior segments of 

 the pregenital part. Only the lobes of the tenth segment 

 project (fig. 7). The first four abdominal segments are 

 normal. The fourth has the sternum prolonged backward. 

 The fifth and sixth segments have the ventral parts small 

 and the terga tapering downward on the sides. The seventh 

 segment is reduced to a narrow ring. 



The hypopygium is small and has the very unusual form 

 shown in figure 2. The principal part is short, but the 

 posterior lower angles are greatly prolonged downward and 

 posteriorly. Each is split into two long cylindrical lobes 

 (fig. 2, d and c?'). 



The eighth segment resembles that of Liancalus hydro- 

 ^hilus, being prolonged ventrally into a tapering point. 

 The paranal lobes of the tenth segment are simple. 



Diaphorus mundus Loew. 

 Plate XXXIII, Fig. i. 



Externally the abdomen of this species is similar to that 

 of Hydrofhorus algens. The hypopygium is not visible, 

 being ordinarily retracted or bent forward into the fifth and 

 sixth segments, and only the tips of the paranal lobes of 

 the tenth segment project. 



The hypopygium itself (ix) is somewhat anomalous. It 

 is cup-shaped, the open face being posterior; the lower 

 edge is longer than the upper, and the anterior end is 

 hemispherical. The cavity of the cup is the genital cham- 

 ber. Each lateral rim bears a wide triangular lobe (^d) 

 projecting posteriorly. From the inner face of each of 

 these lobes a large arm-like appendage extends backward 

 and downward {a). Each appendage bears terminally an 

 inward-curved hook. The penis arises as usual from the 



