444 Mr. David Sharp on the 



group defined in my work on the Dytiscidce ; the under 

 surface has on the breast and basal abdominal segment 

 numerous extremely coarse punctures, the prosternal 

 process is broad and tricarinate, there is a rudimentary 

 abbreviated longitudinal impression near each side of 

 the thorax, so that the insect must be placed between 

 Sections A and C of the group referred to. No con- 

 spicuous sexual distinctions can be observed. 



Found at Chiuzenji, in the lake, on the south side, 

 the fourth week of August, 1881 ; a large variety with 

 all the spots largely developed was found, in three 

 examples, at Sapporo. 



Hyphydriis rivalis. 



A small series of this well-known insect was met with 

 at Sapporo, and a single example at Awomori. These 

 Japanese individuals differ scarcely at all from the North 

 American variety Hydroporus ohesus, Lee. 



Agahus insolitus. 

 Oblongo-ovalis, depressus, nigerrimus, nitidus, antennis, palpis 

 pedibusque anterioribiis rufis, pedibus posterioribus piceis, elytris 

 versus latera guttulis duabus pallidis ; corpore superne obsoletissime 

 reticulato, fere Isevigato, prothoracis margine lateral! crasso. Long. 

 5| mm., lat. 3 mm. 



This is a very abnormal species for a member of the 

 genus Agahvs, the coxal lines being but little turned 

 outwards behind, and the swimming-legs slender, and it 

 has more the aspect of a Platyncctes or Agahinus ; it is, 

 however, connected to a certain extent with the more 

 ordinary Agabi by means of ^. optatns, and the characters 

 therefore are not sufficiently definite to justify the 

 establishment for it of a genus distinct from the poly- 

 morphic Agahus. The outlines of the thorax and elytra 

 are continuous, the hind angles of the former slightly 

 obtuse, the reticulation of the wing-cases is almost 

 obliterated, but the subserial punctures, though fine, are 

 distinct and numerous ; there is a pale spot on each near 

 the side beyond the middle, and a second close to the 

 a])ex. The prosternal process is broad and flat, its 

 anterior portion strongly margined ; the wing of the 

 metasternum is very slender, the rather large hind coxoe 

 and the basal ventral segments are finely strigose. The 



