16 Bulletin American Museum of Natural History [Vol. XLII 



Helophorus and thirty-two in Hydro philus. The number seems to be 

 constant in the Hydrobiinse as all specimens examined had twenty -four 

 styli. Both the meso- and metathorax have a dorsal transverse row of 

 two setae. The wings are folded down over the ventral side of the body 

 and the metathoracic pterothecse may (terrestrial species) or may not 

 (others) be visible from above. The first to seventh abdominal seg- 

 ments each possess, dorsally, a transverse row of four to six styli. The 

 second to seventh abdominal pleurites each bear a stylus. The cerci 

 are present and well developed. 



