1916] Aquatic Hemiptera 363 



degree be deemed a true Gerrine, since they clearly belong to 

 widely dissimilar families. In these three last named divisions, 

 all the claws are apical and well-developed, which is also true 

 of certain Oriental Gerrids, save that the claws in the latter are 

 very small. In all the other water-striders, the GerridcB proper, 

 the claws of the last two pairs of feet at least are subapical and 

 inserted in some sort of a slit. The legs in all are heavily 

 pilose, in some few bristly. In the majority they are very 

 slender and long, except in Microvelia, Rhagovelia and Rheuma- 

 tobates, in which last, in some of the species of the genus, the 

 male femora are apt to be curiously distorted; and in the other 

 two genera much thickened. A description of the process of 

 locomotion in Gerris remigis, Say, our common brown water- 

 strider, may be taken as typical of the family Gerridce. The 

 tarsi only of the first pair of legs touch the water for support. 

 The middle pair is used for propulsion by rowing motions, 

 and with them they take longer or shorter strokes, according 

 to their degree of haste, the tarsi only lying flat upon the surface 

 and more or less outstretched. Steering is done by the hind 

 pair mainly, and at times by a longer or shorter stroke from one 

 or the other of the propelling feet to help. Both the tibia and 

 tarsus of the hind pair touch the surface, the legs trailing behind 

 the bug loosely. In the others, the HalobatincE, including the 

 Rheumatobates and the other lacustrine and oceanic forms, 

 the process has been observed to be the same in some, and 

 probably is in the others, so far as rowing with the middle 

 feet and steering with the hind goes, but no detailed observa- 

 tions seem to have been made in regard to the use of the anterior 

 feet. Nothing appears to be known in this respect about 

 the oceanic forms. Microvelia moves with what Kirkaldy 

 has called a scuttle, that is, a little run in staccato steps, but 

 this is when not in haste. When these tiny bugs are in a hurry, 

 they give long, powerful strokes of the middle legs, and then 

 travel very swiftly. The most peculiar member of the group 

 in regard to adaptation of the organs of locomotion to environ- 

 ment or uses is Rhagovelia. This genus, with two exceptions, 

 by preference frequents the swiftest current of streams, where 

 the waters braid in ripples, and is there to be found in schools, 

 sometimes numbering into the thousands, as I saw them in 

 Mexico, on the shallow Rio Santa Catarina, which runs through 

 the City of Monterey, in the North. In these, their favorite 



