152 THE ENTOMOLOGIST. 



portions of England, and from Lincolnshire to Connemara ; the 

 macropterous form is usually very scarce, though occasionally 

 occurring somewhat plentifully. 



Geeeis, Fabr., 1794,* is the last gymnokeratous genus with 

 which, for the present, we will be concerned. 



The short (compared with that of Hydrometra, Latr.) head, 

 the very long mesosternum, and the very long intermediate pos- 

 terior legs, readily distinguish it from its allies. There are ten 

 British species, forming three well-marked subgenera ; the latter 

 are separable as follows : — 



1. First segment of antennae much longer than 



the second and third together ; nearly as 

 long as second, third, and fourth together 

 (PI. 1, f. 7). [Sixth segment of connexi- 

 vum produced into a long spine] ... Aquarius, Schell. 



— First segment subequal to, or slightly shorter 



than, the second 2 



2. Antennae short, subequal to, or shorter than, 



head and thorax together (PL 1, f. 9) ; 



sixth segment angular, not spinose ... Gerris, in sp. 



— Antennae long (when turned back reaching 



to posterior coxae) (PI. 1, f. 8) ; sixth seg- 

 ment produced into a long curved spine 



Limnoporus, Stal. 



As the habits of the various species appear to be very 

 similar, the following account (drawn up largely from Meinert's 

 paper, confirmed and extended by one or two other small pub- 

 lications and the few observations I have been able to make) is 

 to be taken as applying to any species, unless specially in- 

 dicated: — t 



While Hydrometra and Hydroessa disport themselves almost 

 constantly at the margins of the pond or stream they inhabit, 

 Gerris (and, to some extent, Velia) venture out into the open, 

 though they hold themselves continually in readiness to dart 

 back to the shelter of the shore. 



The legs of Gerris are very remarkable, the two hinder pairs 

 being very long, thin, almost thread-like (filiform), and destitute 

 of the swimming-hairs which are such a marked feature of the 

 more specialised kryptokeratous forms. Such lengthy appen- 

 dages would be a serious obstacle to rapid progression in insects 



* = Aquarius, Schell. 1800= Hydrometra, Fabr., 1803= Tenagogonus, 

 Stal, 1868. The word " Gerris " is doubtless a modification of the Latin 

 Gerres (see Entoni. 1898, p. 103). 



f See Meinert, I. c. pp. 81-100 ; Eeuter, I. c. ; De Geer, 1773, ' Memoires,' 

 hi. pp. 311, et seq. ; Amyot and Serville, 1843, ' Hemipteres,' pp. 409-23 ; 

 Amyot, 1846, Ann. Soc. Ent. France; Miall, 1895, Nat. Hist. Aquat. Ins. 

 pp. 349-51. 



