176 THE ENTOMOLOGIST. 



egg — which is quite different in appearance from that of Gerris, 

 or indeed any other Ehynchoton known to me — is long and 

 spindle-shaped, about two millimeters long, that is to say, 

 about one-half the length of the abdomen. The young nymph 

 emerges seventeen days after oviposition, and is light green in 

 colour. Hydrometra lineata, Say, is carnivorous, its food con- 

 sisting of insects that fall into the water.* "When such a 

 hapless insect falls into the water, it is at once pounced upon by 

 one or several voracious Hydrometras, who insert their beaks and 

 proceed to suck the juices from their still struggling victim. I 

 have seen no less than ten thus surround their prey, all with 

 their heads in the direction of common interest, and their bodies 

 radiating outwards." 



'' The peculiar habitat of Hydrometra, combined with its 

 elongate form, has given rise to a secondary sexual character, 

 which occurs in both H. lineata and H. stagyiorum. This consists 

 of two notched projections on the inner side of the sixth abdo- 

 minal segment, close to the incisure between the sixth and seventh 

 segments. The object of these notched elevations of the abdo- 

 minal walls is to fit over the lateral keels of the female abdomen, 

 thus steadying the abdomen of the male during copulation." 

 Some useful structural details of H. lineata and H. staguorum 

 are figured. 



Some final remarks upon the genus have, however, to be 

 slightly remedied. The "Siberian Hydrometra" jankoivskii, 

 Jakovlev, does not belong to the genus Hydrometra, Latr., but 

 to Hydrometra, Fabr. — that is to say, to Gerris, Fabr., Latr.f 

 The name " lineata,'" moreover, cannot stand, as it is preoccu- 

 pied by H. lineata, Eschsch. (1822, Entomogr. p. 110), from 

 Manilla L? = vittata, Stal, 1870] , and I therefore rename 

 Say's species after the entomologist who has first given some 

 account of its habits : 



Hydrometra martini. Kirk., 1900 



= H. lineata, Say, 1832 [nee Eschsch., 1822]. 



As Mr. Martin has omitted any mention of the species, it 

 may be well to call attention again X to the fact that Hydrometra 

 caraiba, Guer., from the Antilles and Central America, is a true 

 Hydrometra, and not a Gerris as catalogued by Lethierry and 

 Severin. 



- See Entom., 1899, p. 112. 



f H. stagnorum (Linn.) is also recorded from Siberia. See J. Sahlberg, 

 1878, Svensk. Akad. Handl. xvi. no. 4, p. 38. 

 \ See Eevue d'Entom., 1898, p. 73. 



