WATER-STRIDERS, STRIDULIVELIA—DRAKE AND MENKE 415 
apex of the omphalium. The ostiolar sulcus (one on each side) ex- 
tends from the ostiole anteriorly along the side (note angulate projec- 
tion of sulcus on each side) of the omphalium and then curves arcuately 
upwards on the metapleuron in front of and slightly higher than the 
hind acetabulum. The apex of the sulcus is provided with a tuft of 
brownish hairs (pl. 2). 
According to the present authors’ field observations in Panama, 
Trinidad, and Mexico, the members of the subgenus Stridulivelia are 
inhabitants of both small and large streams. The specimens were 
netted in flowing water, mostly among emergent vegetation or close 
to the shore under overhanging vegetation. More than 50 specimens 
of V. tersa were collected in a single school in a very narrow stream in 
Trinidad. 
Key to the Subgenus Stridulivelia of Mexico, Central America, and the 
West Indies 
1. Hind femora and connexiva equipped with stridulatory structures in both sexes 
(pl. 1); male parameres as in plate 3,a . . . Velia tersa Drake and Harris 
Hind femora and connexiva without sound-producing structures (pl. 2,b); 
male parameres asin plate3,b-d.... . OS a2 
2. Abdominal pleurites II-V with median vertical are apical fieeee fifths of 
last antennal segment whitish, testaceous; male parameres as in plate 3,b. 
Velia cinctipes Champion 
Abdominal pleurites IT-111 or II-IV with median vertical furrows; antennal 
segments unicolorous . . . a Msn ties 
3. Abdominal pleurites II-III aa media eenical tartans (ell 2,b); male 
parameres asin plate 3,c ...... . .. . Velia epeixis, new species 
Abdominal pleurites II-IY with median vertical furrows; parameres as in 
Diates Gas. 5 os) Ging, Fueties sew «oa 6 at... \Wela pueblana. Drake 
Velia tersa Drake and Harris 
PLATES 1, 3,a 
Velia tersa Drake and Harris, 1941, Rev. Ent., vol. 12, p. 338. 
BRACHYPTEROUS FORM: Dark reddish brown to chocolate brown, 
with connexiva and appendages yellowish brown; pronotum unicari- 
nate, coarsely punctate, each puncture within clothed with an encir- 
cling row of extremely small silvery hairs, also with a fairly large patch 
of longer silvery hairs in each anterolateral angle of pronotum. 
Length: 4.70-5.00 mm.; width: 1.10-1.35 mm. 
Measurement of antennal segments: I, 1.05 mm.; II, 0.72 mm.; 
III, 0.50 mm.; IV, 0.50 mm. Legs rather slender, with femora only 
slightly incrassate; foretibia with a short dark apical comb; middle 
leg with tarsal segment II much longer than III (50: 30); hind femur 
slightly thicker in male than female, with five or six short spines on 
