b THE ENTOMOLOGIST. 



though much shorter than is usual in the Gymnocerata* (to which 

 Hebras and theGerridae belong), they are not concealed in a groove 

 { fovea) on the under side of the head, thus forming an exception 

 to the general rule among the Cryptocerata. In Ilyocoris 

 (= Naucoris, Saund.) they are somewhat similar to Ajriieloclteinis, 

 but shorter and rather thicker, and the apical segment is very 

 short. In the Nepidae they are very small, so much so that 

 Geoffroy, one of the earliest Linnean writers, made the mistake 

 of supposing the raptorial anterior legs to be the antennae. In 

 Nepa the penultimate segment is laterally produced, on one side 

 only, like a pickaxe, the apical segment being produced, on the 

 same side, in a very similar manner. The foveas, in this genus, 

 are vaulted, probably forming an auditory chamber for the 

 increase of sound-perception. With a slight difference in detail, 

 the antennae of Ranatra are very similar to those of Nepa. In 

 Corixa the antennae are subcylindric, the fourth segment being 

 short and very thin ; in Micronecta the last segment is spindle- 

 shaped, concave beneath. In Plea the third segment is spindle- 

 shaped and convex, the fourth being very small and thicker at 

 the apex than at the base, arising below the apex of the third. 

 In this genus the antennae are clothed with sparse hairs near the 

 apex of each joint. In Notonecta the first segment is very short ; 

 the second is subcylindric, thick ; the third is smaller and slen- 

 derer, shaped somewhat like the blade of a knife ; the fourth 

 smaller and shorter still, but formed like the third. The third 

 segment is furnished with half a dozen or more long clubbed 

 hairs. It is probable that the antennae, in the Cryptocerata at 

 least, are very largely auditory and, to a much less degree, 

 tactile organs. Those of the Cryptocerata are figured in Fieber's 

 ' Genera Hydrocoridum ' (1851, Abhandl. bohni. Gesellsch. 

 Wissensch. (v.), 7, pp. 183-210, Plates 1, 3, & 4). 



The Legs. 



In all the aquatic forms, both gymnoceratous and cryptoce- 

 ratous (with the possible exception of the Corixidse), the anterior 

 legs are raptorial. In all the femora are dilated — in some 

 moderately, in others enormously. In the Hebridae and Gerridae 

 there is little modification, except that in Gerris, Hydroessa 

 (= Microvelia), and Velia the claws are inserted, as also in the 

 posterior pairs, in a cleft below the apex.t 



* yvpvoi; (gumnos), naked, i.e. "not concealed," and xipuiu (Iceraia), 

 antenna ; xpTn-o? (kruptos), concealed. 



f Most authors speak of the claws being "ante-apical" or "inserted 

 above the apex." I regret that I cannot conceive of the claws being inserted 

 above the apex ! As will be noted further on, the genera with subapical 

 claws form the genuine Gerridae ; the others — viz. Aepophilus, Hydrometra, 

 Mesovelia — are probably more nearly allied to Hebrus. 



