102 THE ENTOMOLOGIST. 



Length 13 mm., first antennal segment four times as long as 

 second ; anterior femora incrassate, cylindrical, one-fourteenth longer 

 than tibiae, which are five-sixths longer than tarsi ; ventral surface 

 covered with lilac-grey pubescence. (Colombia.) - 2. baked, Kirk. 



The introduction of this new species necessitates some modi- 

 fication of Mayr's generic diagnosis (Verh. Ges. Wien, 1865, 

 p. 445 ; and Novara Exped., Hem., p. 178). The description of 

 the antennae and the mention of the length-equality of the ante- 

 rior tarsal segments must be removed to the specific diagnosis 

 of B. albinervus. 



It is difficult to state a generic diagnosis that will succinctly 

 distinguish Brachymetra from the other Halobatinse. Bianchi 

 gives the following characters (Ann. Mus. Zool. Petersb. 1896, 

 p. 71):— First antennal segment shorter than the other three 

 together, fourth not longer than third ; anterior tarsal segments 

 subequal ; intermediate and posterior tibiae and tarsi not ciliate. 

 The last character eliminates Halobatcs, Eschsch. 



Unfortunately the third and fourth segments of the only- 

 remaining antenna are missing in B. bakcri ; but, as the first 

 segment is four times as long as the second, I doubt very much 

 the stability of Bianchi's first character (shown in Mayr's 

 excellent figure of B. albinervus). The anterior tarsal segments 

 in B. bakeri are, as shown above, distinctly unequal. 



The other Halobatine genera differ as follows: — Hermatobates, 

 Carp., is at once distinguished by the greatly incrassate and 

 laterally-dilated anterior femora, and by the trisegmentate tarsi ; 

 in Metrobates, Uhl., and Platygerris, E. B. White, the first seg- 

 ment of the anterior tarsi is very much shorter than the second ; 

 while in Putamometra, Bianchi, Trepobates, Uhl., and Chimar- 

 rhometra, Bianchi, it is much longer ; moreover the anterior 

 femora of Trepobates are not incrassate. 



The nearest ally, Metrocoris, Mayr, has the anterior margin 

 of the pronotum strongly excavated, the basal process of the 

 pronotum triangularly produced (not rounded), and the first 

 segment of the anterior tarsi much shorter than the second. 



Having regard to the specific variation in the proportions of 

 the antennas in the extensive genus Gerris, Fabr., it would seem 

 well not to base other genera of the Hydrometridae principally 

 upon such proportions. 



The length of the abdomen in Brachymetra (in both species 

 the length of the head and pronotum combined is subequal to 

 that of the abdomen) gives this genus a general aspect very 

 different from most of the other genera of the Halobatinse, 

 approaching in this respect the Gerrinas. 



2. Gerris, Fabr. 

 In the third volume of Lethierry and Severin's Catalogue, 

 Gerris is used as if it were feminine. It is presumably derived 



