144 HEMIPTERA-HETEROPTERA. 
Unknown to me. Described from an apterous specimen, presumably a male. The 
insect is 74 millim. long, black, with the usual silvery-pubescent markings; the legs 
are brown, paler beneath and at the base of the anterior femora; the posterior femora 
are armed with two spines on the inner side beyond the middle; the antenne* are 
long and slender, with joints 1 and 2 subequal in length. 
Subfam. GERRINA. 
The subfamily Gerrine is usually divided into two groups t, characterized by the 
relative length of the abdomen, the latter being very short in the pelagic Halobates 
and its allies. This character, however, is so unsatisfactory that it cannot be used— 
Brachymetra having the abdomen scarcely shorter than in some species of Gerris, and 
Potamobates being closely related in other respects to Platygerris. In the last-mentioned 
genera the genital segments of the males are asymmetrically formed, these segments 
being furnished with angular or dentiform processes on one side of the body only. 
Halobates occurs in the vicinity of the Atlantic and Pacific coasts of Central America, 
and I have seen one species in plenty on the surface of the sea, in the Gulf of Nicoya, 
Costa Rica; but as the marine forms are excluded from the scope of this work, nothing 
more need be said about it. 
GERRIS. 
Gerris, Fabricius, Ent. Syst. iv. p. 187 (1794) (part.); Amyot et Serville, Hist. Nat. Ins. Hémipt. 
p. 414. 
Aquarius, Schellenberg, Das Geschl. Land- und Wasserwanzen, p. 25 (1800). 
Hydrometra, Fabricius, Syst. Rhyng. p. 256 (1803) (nec Latreille) ; Fieber, Europ. Hemipt. 
pp. 33, 106. 
Tenagogonus, Stal, Ofv. Vet.-Ak. Férh. x. p. 263 (1853); Hemipt. Afric. iii. p. 168. 
Limnotrechus, Stal, Ofv. Vet.-Ak. Férh. xxv. p. 895 (1868). 
Hygrotrechus, Stal, loc. cit. 
Five species from Central America are here referred to Gerris, in the wide sense: 
two of these belong to the section MHygrotrechus, which includes the European 
G. paludum, Fabr., and G. najas, De Geer; the three others to Limnotrechus. Limno- 
metra, Mayr, and Limnogonus, Stal, are retained, each with two Central-American 
species; Zenagogonus, Stal, ought, perhaps, to be adopted in place of one of these 
names, but as Stal subsequently used Tenagogonus for Gerris in the wide sense, it is 
best dropped #. 
The species here referred to Gerris have the two joints of the anterior tarsi subequal 
in length. 
* Five joints are mentioned, the minute jointlet between the second and third being counted as a truc joint. 
+ Cf. Bianchi, Ann. Mus. Zool. St. Pétersb. 1896, pp. 70, 71. 
t In his first paper no type is mentioned. 
