252 NATURAL HISTORY OF ARTHROPODS. 



Their eyes are large, reniforrn, twice sinuated on the outer side, and project a little 

 way over the front margin of the prothorax. The rostrum is elongate, conical, acute, 

 and composed of four joints. Ocelli are absent ; the vertex is a broad 

 wedge with the narrow end behind, and the face curves downwards. 

 The prothorax is transverse, moderately convex, gradually narrows 

 anteriorly, and has the lateral margins sharp, projecting. Next the 

 lower sinus of the eyes, the tapering antenna? project upwards, and are 

 formed of four joints, of which the basal one is very short, the second 

 long, stout, rounded, the third still longer, fusiform, narrower at tip, and 

 fringed with curved bristles. The membrane is here well distinguished 

 from the corium, and the legs are all long ; the tarsi are three-jointed, 

 with the basal joint minute, and armed with two slender, curved nails, 

 ^ diffe 1 ' 61 ^ lengths, on the anterior and intermediate hairs ; the pos- 

 terior pair of legs is longest, somewhat flattened for swimming, and 

 thickly fringed with long silky hairs on both margins of the tibia? and tarsi. On the 

 middle line the venter is distinctly ridged, and invested with long hairs. 



Several genera have been defined in this family, but only three are well known in 

 North America. The first and commonest of these is Notonecta, which may be known 

 from the other genera by the distinctly marked membrane, by the broad body accom- 

 panied by a scutellum about as wide as the pronotum, and by the narrow curved front, 

 without swelling or prolongation. The common N". undulata is widely distributed in 

 North America, and is a very variable species. Some specimens are nearly all ivory 

 white above, with the dark dorsolum showing through the base of the prothorax, with 

 dark brown eyes, and some dark cloud-like patches on the sternum and venter. More 

 commonly it has a broad, zigzag, interrupted black band across the base of the mem- 

 brane, and one or two oblique streaks nearer the base of the corium, occasionally also 

 on the inner margin of the clavus. The disc of scutellum, dorsum of the abdomen, 

 and sutural margins of the ventral segments are also often black. It measures one- 

 third to nearly one-half of an inch in length, and inhabits muddy pools, ponds, and 

 bodies of still water in most parts of the eastern United States, and extends southwest 

 into Mexico. Various other species inhabit America, one or more occurring in every 

 country as far south as Patagonia. Several others belong to Europe, Asia, and 

 northern Africa, but the most beautiful of all is the N~. mexicana. This is a large, 

 robust species, with bright red wing-covers, black membrane and scutellum, and ivory 

 yellow prothorax, head, and legs. A variety occurs in which most of the red color is 

 replaced by black, or yellow and black in unequal proportions. It measures fully one- 

 half of an inch in length, and is distributed from southern Mexico to central Arizona. 

 Most of the species already known have a white or pale ground color, marked 

 with yellow, black, and smoky brown, and those of Europe, while being specifically 

 distinct, offer varieties similar in pattern to those of the United States. All are capa- 

 ble of sustained flight, and often go long distances in search of a congenial body of 

 water when the food gives out or the water shallows in the place where they were born. 

 The incessant activity of these insects in the water is very remarkable ; from early 

 morning until sundown, and even later, they are rising with sudden jerks from the 

 bottom to the surface, and then diving with the hind-legs in rapid motion. A spray 

 of grass or projecting stick at the top of the water serves as a balancing point by which 

 to sustain themselves at pleasure. Their appetite, also, seems almost insatiable. 

 Every insect that they can overcome falls a prey to their quick grasp, and when once 



