They are formed for creeping, and not for 

 swimming; the body is but httle heavier than 

 water; and, unless they are placed upon a 

 rough surface, they can scarcely progress, as 

 the motion of the feet tends to throw them 

 from the bottom. In a glass vessel, whether 

 they are upon the bottom, or falling through 

 the water, they appear to be quite helpless. 



All the tarsi are cleft, each toe [phalanx, 

 Burm.) being furnished with a perfectly retrac- 

 tile, bifid unguis, a secondary claw arising from 

 the concavity of the primary one, and lying in 

 the same plane with it, as in some coleopterous 

 genera. Fig. 5a represents one of the two 

 claws extended, and 56 half retracted. The 

 foot is very sparsely bristled, or not at all. 



The species, except 3,? 7, 8, are from the 

 Susquehanna. I have referred them to a new 

 genus, only provisionally; as I cannot learn to 

 what genus Hydrachnae grossipes et longipes, 

 Mliller, (with which they appear to be con- 

 generic,) are referred by modern authors. 



The palpi, fig. 3, 4a (except the point of 



