HUNGERFORD: AQUATIC HEMIPTERA. 91 
_ three together, the outer third tapering asymmetrically to tip. Limbs are 
stout, and tarsi one-segmented, ending in two apical claws. A single 
_ dorsal pore on the anterior margin in the median line of the fourth ab- 
dominal segment. 
Morphological studies. Aside from the external structures studied by 
taxonomists, no morphological work has come to the attention of the 
writer. 
Family HYDROMETRIDZ Billb. 1820. 
Limnobatidce Fieb. 1851. 
A. TAXONOMY OF HYDROMETRIDA. 
Family Characteristics. Exceedingly slender bugs of a dark color that 
dwell upon the shores and floating vegetation of the water. The adults 
_ are dimorphic in respect to wings. The apterous forms are perhaps more 
common than the winged, especially in the north. The head is as long as 
the entire thorax, though it too is elongate. Ocelli absent; eyes distant 
from the anterior margin of the thorax; antenne four segmented, fili- 
form; rostrum three segmented; tarsi three segmented. One genus and 
two species in America. At least a dozen species in the world. 
Historical Review. Since the genus Hydrometra was established in 
1801, these strange bugs have been known best, in this country at least, 
by the name of Limnobates, which translated into English means marsh- 
_ treaders. This name was assigned to them by Burmeister in 1835. Most 
- of the European notes deal with the species H. stagnorum. Long before 
this time, however, we can identify these insects in the literature. Swam- 
merdam 1737 (Hill’s Trans. 1758), in speaking of ‘water Tipula,” 
which he says are worthy of the greatest attention, on account of the 
_ wonderful lightness wherewith they run on the surface of the water,” 
- mentions a species of this insect, which is “of a wonderful delicacy and 
of a very singular structure and very slow paced.” This, I take it, is 
_ Hydrometra. De Geer, 1752, figures a Hydrometrid under the name of 
_ Cimex acus, while Geoffrey calls it “La Punaise aiguille.” It is indeed 
_ slender like a needle. Linnzus placed the then known form stagnorum, 
- which he described, in the genus Cimex. Lamarck is credited by Van 
. Duzee with the generic name of Hydrometra, 1801. 
Genus HYDROMETRA, Lam. 
Sufficiently characterized by the family description for the present. 
4 Two species are listed for this country. They may be separated by the 
- following characters taken from the writings of Kirkaldy and Bueno. 
KEY TO HYDROMETRA. 
A. Terminal segment of male (from above abruptly enlarged at tip and 
bearing a well-marked spiniferous tubercle. Caudal margin of this 
genital segment sinuate in lateral views. H. martini Kirk. 
. Terminal segment of male (from above) swollen in outer half but 
not abruptly so. Spiniferous tubercle lacking or not prominent. 
H. australis Say. 
