AN INTERESTING NEW WATER STRIDER 

 FROM FORMOSA 



By Teiso Esaki 

 the Zoological Institute, Science College, Imperial University, 



During a trip to Formosa, I made a collection of insects on 

 September 25, 1921, at Sosan near Taihoku, with Mr. Ryoichi 

 Takahashi, of the section of applied zoology, Department of 

 Agriculture, Government Research Institute of Formosa. In 

 the collection I have found a species of the family Gerridae, 

 interesting both systematically and ecologically. A small number 

 of the same species, moreover, were captured by us at Shinten 

 near Taihoku, several days later; also two specimens, collected 

 by the late I. Nitobe at Kusukusu near Koshun, were found in 

 the collection kept at the Government Research Institute of For- 

 mosa in Taihoku. This insect was subsequently found to be new 

 to science, and to belong to a new genus. 



Genus RHYACOBATES novum 



Head longer than broad between eyes, the latter being moder- 

 ately emarginate interiorly; portion of head in front of eyes 

 extended and longer than rest of head, almost pentagonal in 

 shape; antennae not longer than body, with first joint much 

 longer than the three other joints together, second and fourth 

 joints subequal in length, third slightly longer; rostrum scarcely 

 passing anterior coxae. 



Pronotum much shorter than head, anterior margin straight, 

 posterior slightly concave ; mesonotum about three times as long 

 as pronotum; anterior femora thickened and longer than tibiae, 

 the last with a distinct apical spine; intermediate and posterior 

 femora about subequal in length, very slender, a little shorter 

 than twice the length of intermediate tibiae in the former, while 

 in the latter about three times as long as posterior tibiae. Inter- 

 mediate tibiae with a fringe of long hairs. First intermediate 

 tarsal joint about eight times the length of second; posterior 

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