24 THE VOYAGE OF H.M.S. CHALLENGER. 



Eyes large, situated at the back of the head, and resting partly on the pronotum. 

 ProtJiorax transverse, much broader than long, not confluent with the mesothorax. 

 Mesothorax and metathorax together cylindrical, coalescent, the boundary 



between them scarcely distinguishable ; no scutellum nor scutellar process. 

 Elytra and wings always wanting. 

 Front legs short, rather stout. Tibia with a triangular process near the apex. 



Tarsus two-jointed ; second joint with claws inserted about the middle. 

 Middle and hirid legs long and slender, inserted at the sides of the posterior end 



of the thorax ; the hind legs inserted above the middle legs. Middle legs 



with tibia and first joint of tarsus furnished with a fringe of long hairs ; 



tarsus two-jointed, the second joint clawed before the tip. Hind legs with 



one-jointed tarsus clawed before the tip. 

 Abdomen very short, first three segments covered above by the metanotum. 



Apex of the abdomen in the male with a conspicuous rhomboidal appendage. 



DETAILS OF STRUCTURE. 



Halohates presents a peculiar appearance on account of the great development of the 

 thorax in comparison with the abdomen, thus approaching in facies the larvse of some 

 other genera of Hydrohatina. The body is covered with very short and close pubes- 

 cence of a grey colour, which is the predominating tint of the species, few of which have 

 any conspicuous markings, at least on the upper surface. In all there are two reddish 

 or yellowish spots at the back of the head, but in most cases these are not conspicuous. 

 Several of the species have pale markings on the under side. 



The Head and its Appendages. 



Tlie Head viewed from above is shortly triangular ; viewed from the side, the vertex 

 is more or less convex, while the frons is sloped very much downwards. The vertex is 

 convex, at least in the middle, but is usually widely but shallowly depressed on each 

 side near the hind margin ; while there is another more slight depression before the 

 middle lobe of the face. In the female the latter depression is more conspicuous than in 

 the male. The posterior depressions do not extend so far as the orbits, the inner sides of 

 which are slightly tumid. In the posterior depressions is generally a rufous spot, usually 

 ill-defined and not conspicuous, but forming in a few species a conspicuous, oblique, 

 reddish-yellow mark on each side of the middle of the back of the head. The hind 

 margin between the eyes is convexly rounded, and in one or two species the edge is more 

 or less narrowly elevated. The front of the head is sloped downwards, and is nearly, but 



