272 NATURAL HISTORY OF ARTHROPODS. 



of tarsal joints is variable, some having two, others three joints ; a few genera have 

 only one to the fore-tarsi. This group is composed of mostly small, or even minute 

 insects, the longest of which do not exceed one-third of an inch in length. 



A common North American form is the Rhar/ovelia obesa. As a genus, it is dis- 

 tinguished from Velia by the blunt forehead, and by the ajjical tarsal joint of the 

 middle feet, which last is slender, spindle-shaped, split to next the base, and at that 

 point the slender claws are attached. It is of a bronze-black color, with the upper 

 part of the abdomen and legs highly polislied, the latter metallic green, and the hind 

 thighs of the male much thicker than those of the female, armed beneath with a series 

 of sharp teeth, the innermost one forming a longer sjjur; the middle tibiae are nearly 

 cylindrical, a little tapering at tip, and armed on the inner side with close-set, very 

 short teeth. The abdomen of the female appears pinched behind, so that the lateral 

 ridges are brought in contact on the middle line. The base of the antennas, two oval 

 spots on the front sub-margin of the prothorax, coxse, and hind margin of the middle 

 and posterior acetabular caps are pale yellow. The rostrum is piceous, paler at base, 

 reaches to the middle coxse, and is very acute. All over the upper surface of the 

 winged form a fine brown pubescence is conspicuous, which is much less observable in 

 the unwinged, and easily rubs off. A beautiful, silky, white sheen decorates the pale 

 blue color of the venter in both states. The wing-covers are dark brown, gradually 

 widening towards the tip ; the corium grades into the membrane, and the discoidal cell is 

 angular, and connected at each end with another angular cell, bounded by stout veins. 

 These wing-covers are sharply bounded by, and set between, the carinately raised con- 

 nexiva, which are often of a bright orange color. Both sexes of the winged form have 

 a carinate line on the middle of the mesothorax, and this in the female is produced 

 into a slender process, which has a blunt fork -at the tip. The end of the last abdomi- 

 nal segment is acutely produced in the winged specimens, but much less so in the 

 unwinged ones. 



This plain colored but interesting species inhabits the eastern side of the continent 

 from Lower Canada to southern Florida, and westward into Texas. In the Middle 

 States it has not yet been found winged, but in eastern Tennessee, North Carolinn, 

 South Carolina, and Florida the winged form is common in company with the 

 unwinged. They walk over the water with the greatest facility, and often use the 

 longer middle legs like oars, with somewhat of a rowing motion. It is interesting 

 to observe them on the quiet surfaces of the creeks and branches, where they love to 

 remain in groups, staying together motionless for hours at a time, and then gliding 

 away in all directions when startled by the approach of some disturbing object. 

 Mhagovelia is confined to the new world, and several larger species than the fore- 

 going inhabit the West Indies, Mexico, Central America, and Brazil. 



Next to these comes the genus Velia, which is represented by several species in 

 South America and Mexico, and by two others in Europe. In this genus the fore- 

 head is produced forwards, somewhat in the shape of a blunt cone ; the antennre are 

 longer and more slender than in the preceding, and the two apical joints are long, 

 much more slender than the others, and the third joint is longer than either the 

 second or fourth. The first joint of the fore-tarsi is quite short, while the two poste- 

 rior tarsi are long, with cylindrical joints, and the nails are placed on the tip. The 

 mesonotal plate is long, triangular behind, and carried pretty far back over the base of 

 the wing-covers. These last are also furnished with three cells along the middle, 

 between the base and the tip, and the corium is tolerably well distinguished from the 



