THE MARSH-TREADERS. 965 



I. Hydrometra Lamarck, 1801, 295. 



Our species of this genus, characterized as above, have the 

 head widened near tip, narrower in front of eyes; joint 1 of 

 antennas surpassing the blunt-tipped tylus by half its length, 

 2 and 4 subequal, each about half the length of 3 ; pronotum 

 elongate-oblong, somewhat narrowed in front ; elytra, when 

 present, long, narrow, gradually slightly widening behind, their 

 tips rounded, disk with two long veins and two cross nervures 

 enclosing a single irregular cell on apical half; abdomen re- 

 flexed above, convex beneath, its margins parallel, male, mod- 

 erately broadly curved, female. Three species are known from 

 this country, two occurring in our territory. The males of 

 these are easily separated, the females more difficult. 



KEY TO EASTERN' SPECIES OF HYDROMETRA. 



a. Pits on sides above middle coxae two; head in front of eyes 1.3 — 1.5 

 mm. in length; male with under side of sixth ventral with two 

 transverse concave subbasal elevations and last dorsal with a dis- 

 tinct spinous projection. 1104. martini. 

 aa. Pits on sides above middle coxae four; head in front of eyes 1.8 — 2 

 mm. in length; male with under side of sixth ventral with two 

 conical tubercles and last dorsal prolonged as a tubercle. 



1105. AUSTRALIS. 



1104 (1281). Hydrometra martini Kirkaldy, 1900, 175. 



Dark chestnut- or fuscous-brown, often with a bluish tinge; elytra 

 dusky whitish with dark nervures; pronotum with a vague median 

 longitudinal whitish line; antenna? reddish-brown, darker toward apex; 

 beak, legs, under surface and middle of dorsum brownish-yellow; apical 

 halves of tibiae and tarsi more or less fuscous. Apical third of head less 

 widened than in australis. Elytra, macropterous form, reaching sixth 

 dorsal, male; fifth dorsal, female. Length, 8 — 11 mm. (Fig. 192). 



Marion and Lawrence counties, Ind., April 11 — May 11. Ft. 

 Myers, Kissimmee, R. P. Park and Dunedin, Fla., Nov. 24 — 

 April 23 (W. S.B.). Sherborn, Mass., Aug. 30 (Frost). Ap- 

 parently scarce in Indiana, where it has been found only in or 

 about ponds partially covered with duckweed (Latvia) in dense 

 woodland. Common about Dunedin in ponds and ditches or 

 beneath boards and other cover along their margins. When 

 fresh from the last moult the young adult is usually covered 

 with a slate-blue "bloom" which disappears in a few weeks. 

 Although so slender in form, the adults are often attacked by 

 a red mite. But two of the 25 specimens at hand are macrop- 

 terous. The known range of H. martini extends from Ontario 



