OF WASHINGTON. 



85 



taining what the sexual differences in these large Belostomatidae 

 were, and have recently had specimens of Benacus softened and 

 dissected with a view of ascertaining. These examinations show 

 conclusively that both sexes occur in Benacus proper, and that 

 the differences between the two genera are, therefore, not sexual. 

 The only external indication of the sexes is that the tip of the 

 abdomen in the male is whole, while in the female it is slightly 

 notched, and with a small thorn on either end of the notch. 

 There is no difference in the length of the long appendages 

 nor in their shape, but the genital hooks and the cerci of the 

 male are well pronounced and are replaced in the female by mere 

 plates. Specimens illustrat 

 ing these structures are here 

 with exhibited. Seven 

 species of Belostoma are 

 recognized by Uhler from 

 the United States and the 

 West Indies, while in the 

 genus Benacus we have but 

 the one species. Say de 

 scribes his Belostomagrisea 

 as "beneath with three black 

 ish vittae." This points to 

 Benacus, and Uhler has so 

 included it in his check list. 

 Otherwise Say's description 

 would not indicate which of 

 the two insects he had refer 

 ence to. Stal took Say's 

 species to be the northern 

 species of Belostoma {sensu 

 strict o) and therefore kept 

 Leidy's name haldemanus 

 for Benacus. I once sent 

 specimens of Benacus griseus to Prof. Montandon, who corrected 

 the name to Benacus haldemanus, evidently accepting Stal's de 

 termination. Packard in his " Guide to the Study of Insects," 

 page 537, mentions the two species as follows: "Belostoma 

 Jialdemanum Leidy is not uncommon in our waters. It is 3^ 

 inches in length and has black patches on the under side of 

 the body, while in B. grisea Say the under side is unspotted." 

 The first reference is undoubtedly to Benactts griseus, and the 

 second to Belostoma americanum. I refer to Packard because 

 his statement indicates how very generally the two insects were 

 confounded by entomologists, so that even in our leading Guide 



FIG. 4. BELOSTOMA AMERICANUM : a, front leg; 

 b, front tibia and tarsus ; c, tip of abdomen of 

 female, dorsal view, with wings and dorsal mem 

 brane removed ; d, genetalia of same, lateral 

 view; e t f, same parts of male. 



