HEMIPTEEA— HETEEOPTERA— HTDROBATIDiE. 351 



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Hydrometra In the European Tertiaries Germar figures two insects he 

 regards as immature and as belonging to Hydrometra or Halobates, or both, 

 and which also appear to belong to this famil3\ Burmeister further says 

 that Serres mentions a "characteristic Hydrometra" from Aix, but as a 

 comparison will show, he has evidently written Hydrometra for Ploiaria, 

 and that is quite another insect. In our own country we have a couple of 

 species from Wyoming and British Columbia belonging to an extinct genus, 

 Telmatrechus, described below, related to Hygrotrechus, found in the 

 North Temperate zone of both worlds ; and a species of Metrobates, a • 

 genus peculiar to eastern North America. 



TELMATRECHUS gen. nov. {riXfia, rpt'xco). 



This genus is closely allied to Hygrotrechus Stal, and, combining as 

 it does many of the features of this genus and Limnotrechus Stal, may well 

 have been the lineal predecessor of both. The antenna? have the first joint 

 only a little longer than the second. The eyes are not at all prominent. 

 The thorax is relatively shorter than in Hygrotrechus. The legs are very 

 long, the tibiffi of each pair of legs about as long as the femora of the same 

 legs, an equality which I have not found in any other genera of Hydro- 

 batidte ; in the fore legs the equality is perfect ; in the middle legs the 

 tibise are slightly longer, in the hind legs slightly shorter, than the femora ; 

 the hind femora are slightly longer than the middle pair ; so far as can be 

 told from the imperfect remains the tarsi of the middle and hind legs are 

 very much shorter than, not a half or probably a third the length of, their 

 respective tibiae. The posterior lateral edges of the sixth abdominal seg- 

 ment are produced to a tooth precisely as in Limnoti-echus. 



Two species are found in the western Tertiaries. 



Table of the species of Telmatrechus. 



Body stont, with almost regnlarly tapering abdomen 1. T. stali. 



Body slender, with nearly equal abdomen, tapering distinctly only at the extremity. ..2. T. parallelus. 



1. Telmatrechus stall 



PI.- 2, Figs. 11, 12. 

 Hygrotrechus stali Scudd., Rep. Progr. Geol. Surv. Can., 1877-1878, 183-184B (1879). 



The thorax seems to be shorter than in Hygrotrechus, with the limits 

 of the prosternum more visibly marked from above ; the eyes do not ap- 

 pear to be so prominent, and the first antennal joint would seem, from the 



