84 ENTOMOLOGICAL SOCIETY 



Belostoma grande, and, further, that of late years it has come 

 to be known that this was not the true grande, and that the com 

 monest species we have belongs to Stal's genus Benacus and is 

 Say's griseus. This is undoubtedly the common species in this 

 section and throughout the larger portion of the United States, 

 and has received a number of different names, as haldemanus 

 Leidy, harpax Stal, ruficeps Dufour, distinctum Dufour, 

 angustatum Guer. The Belostoma is a relatively rare form, 

 judging from the material in the National Museum, and has also 

 received various names, as impresswn Haldeman, litigiosum 

 Dufour, and obscurum Dufour, all of these being synonyms 

 given in Uhler's list. Stal established the genus Benacus in 1861 

 in " Oversigt Vetenskaps-akademiens Forhandlingar," XVIII, 

 Stockholm, upon Belostoma haldemanum Leidy, which was 

 described in 1847 (Journal Acad. Phil., New Series I, page 59). 

 Stal's diagnosis is as follows : 



Belostoma Latr. " Femoribus anticis subtus sulcatis. Arti- 

 culo basali tarsorum anticorum secundo multo breviore." 



Benacus Stal. "Femoribus anticis pro receptione tibiarum 

 haud sulcatis; tarsis anticis articulis aequilongis." 



Both characters are obvious upon careful examination, but I 

 may add that the front femora of Belostoma are bisulcate their 

 whole length, and that the front tibiae are deeply unisulcate. The 

 two sharp edges of the tibiae fit into the two furrows of the femur 

 when folded together. Benacus has, on the contrary, both 

 femora and tibiae rounded. The two genera, as exemplified by 

 these two common species, are otherwise very similar and easily 

 mistaken for each other. Benacus on the average is somewhat 

 larger in size and with the body more distinctly widened at the 

 basal third. The paler coloring of the side margins of the thorax 

 and the median vitta are, as a rule, more distinctly relieved and 

 more or less ferruginous. Ventrally there are usually two sub- 

 lateral black stripes. The legs are usually unicolorous and the 

 hind tibiae and tarsi are more expanded than in Belostoma. I 

 notice also that in Belostoma, in all the species represented in 

 the National Museum collection, the middle and hind tibiae are 

 usually spotted or banded. All the mere colorational characters, 

 however, vary considerably, and realizing the great variation and 

 especially the great sexual differences that occur in many of the 

 aquatic Heteroptera, which is particularly exemplified in Rheu- 

 matobates rileyi, it occurred to me that the supposed generic 

 differences might possibly be sexual. This suspicion appeared 

 to me all the more plausible from the fact that, in looking over 

 the literature at hand, I could not find that the sexual differences 

 had been pointed out. I was, therefore, quite interested in ascer- 



