Occasional Papers of the Miisciiiii of Zoology g 



4. Apical abdominal appendages long and slender, not retrac- 



tile; hind legs not tiattened ; bodj^ long and slender (in 



our forms) Nepiuar 



Apical abdominal appendages short and flattened, retractile ; 



hind legs distinctly flattened ; body broad and flat 



Belostomatidae 



5. Head shorter than thorax and scutellum together, eyes close 



to thorax 6 



Head as long as thorax and scutellum together, much pro- 

 duced in front of eyes, which are remote from thorax ; 

 body very slender ; usually wingless HydromETRidae 



6. Claws of at least the front tarsi distinctly subapical, with the 



terminal tarsal segment more or less cleft at tip 7 



All tarsal claws situated apically 8 



7. Hind femora (except in females of Rheumatobates) distinctly 



surpassing apex of abdomen; bases of antennae more or 



less remote from eyes, and anterior to them Gerridae 



Hind femora not or barely surpassing apex of abdomen ; bases 

 of antennae (in our forms, at least) contiguous to eyes or 

 located beneath them VeliidaE 



8. Uusually apterous ; hemelytra when present with clavus mem- 



branous, similar in texture to membrane, the latter with- 

 out veins ; body flattened above, convex below ; color usu- 

 ally green; length about 3 mm.; live on surface of water 



or on floating vegetation MesovELIIDAE 



Usually winged ; clavus not membranous, membrane with four 

 or five long closed cells; color not green; size larger; tylus 

 separated from frons by an impressed line ; littoral forms, 

 rarely found in same situations as the ^lesoveliidae. . . .Sai.didae 



Family Hydrometridae, the AIarsh-treaders 

 This family is represented in ^Michigan by a single species. 



Genus Hydrometra Latreilee 

 I. Hydrometra martini Kirkaldy. This interesting species 

 was found in considerable nimibers at two of the beach pools 

 (Stations V and VI) and at Station XII, and a few individuals 

 were taken at Station IX, where they were found on the sur- 

 face of the water under the overhanging Chamaedaphne at the 

 edge of the pond. Although fairly common in July, only a 

 few individuals were seen in August. A single winged speci- 

 men was taken at Station \1 on July 9, 1918. 



