18 BULLETIN 6.3, UNITED STATES NATIONAL MUSEUM. 



The thinl is O.C) nun. above the basal angle of the third ventral 

 (second visi])le) segment. 



The fo}irfh innnediately above and close to the inner membranous 

 edge and basal angle of fourth ventral (third visible) segment. 



The fifth is in the same position relative to the fifth ventral (fourth 

 visible.) segment, and only partl}^ visible without traction on the 

 sixth tergite or a voluntary extension of the same by the insect. 



The sixth is in the same position relative to the sixth ventral (fiftli 

 visible) segment as the fourth, but entirely invisible without trac- 

 tion on the sixth tergite. It is distinctly smaller than the other 

 stigmata and is overlapped by the lateral fold or edge of the sixth 

 tergite and also by the apical fold of the fifth. At this point the 



The tergite of the sixth segment (Plate 7, figs. 2/> and ^p) iw 

 the other segments. 



The first three pairs of stigmata are the largest, the fourth and 

 fifth are slightly smaller. 



The tergite of the sixth segment (Plate T, figs, ^p and 4p) is 

 moderately chitinized and flexible, evenly and arcuately rounded at 

 apex, the margin set Avith short setse and sparsely so over the dorsal 

 surface apically. 



The sternite is strongly and firmly chitinized and constitutes the 

 so-called fifth Adsible ventral segment. 



Retractile segments. — Four in number and homologous to those of 

 Hydro philus piceus as figured by Packard.* 



Secenth segment. — The tergite and sternite are chitinized and very 

 flexible. The tergite is short, broadly, and not strongly arcuate at 

 apex, most strongly chitinized laterally and quite membranous at 

 middle; margin frimbriate with short setse and the dorsal surface 

 sparsely pubescent. (Plate 7, figs. 2r and 4r.) 



The lateral angles at base articulate with the lateral and basal 

 angles of the sternite and in both sclerites these angles are more 

 strongly chitinous than the other parts of the same sclerite. This 

 articulation is stronger in the male. 



The sternite is different in the sexes. (See figs. 2 and ."), Plate 2, 

 and figs. \e and So, Plate 7.) In the male it is bilobed and described 

 in detail for each species in the body of this work; in the female 

 it is broadly arcuate at apex, in the male deeply emarginate between 

 the lobes. 



In both sexes each lateral moiety is made up of a triangular 

 chitinous plate, which at the external and internal basal angles are 

 more or less produced. In the male the internal and more or less 

 anteriorly produced angles are separate and not connate — so as to 

 permit of the abduction and adduction of the lobes which no doubt 



« Text-Book Ent., p. 181. 



