STUDIES IN AUSTRALIAN AQUATIC HEMIPTERA. 



No. II. 

 By HERBERT M. HALE, South Australian Museum. 



Family NOTONECTIDAE. 



Plates x-xi and Text fig. 361-373. 



The salient characteristic of the bugs comprising this family is a curious habit 

 of swimming with the venter uppermost, hence their popular name "back- 

 swimmers." The underside of the abdomen has a median, longitudinal keel, 

 with a trough on each side, over which guard hairs close and imprison the air 

 which is utilized during submergence. The back is very convex longitudinally, 

 so that the thorax is relatively deeper than in other aquatic forms. All the tarsi 

 terminate in two claws and are usually two-jointed ; in the male of Anisops the 

 anterior tarsi have but one joint, and in the Plea herein described, both the 

 anterior and intermediate tarsi are monomerous. 



Four genera are recorded from Australia, but of these Anisops occurs far 

 more commonly than the others, which are represented each by one species only. 



Specific Characters. The general size of the head and the comparative 

 width of the dorsal interocular space furnish useful and readily recognized 

 characters in the determination of our species ; in this connection the terminology 

 given by Kirkaldy in his "Revision of the Notonectidae, No. 1" (^) is here 

 adopted. The whole of the dorsal interocular surface is called by this author 

 the "notocephalon," the term "vertex" is restricted in its usage to define the 

 apparent anterior margin of the notocephalon, while the distance between the 

 posterior angles of the eyes is aptly termed the "sjnithlipsis"; Kirkaldy later 

 applied this word to a genus of Australian Mirid bugs. As a rule the inner 

 margins of the large eyes diverge more or less from the base of the head and 

 converge slightly towards the front of the notocephalon, so that the vertex is not 

 actually the widest interocular space. 



Colour is ill most cases a character of little assistance; the notocephalon is 

 ochraceous or testaceous in dried specimens, and the legs are generally' of like 

 colour, with parts of the inner or lower surfaces more or less dark brown to black. 

 The species herein dealt wdth are structurally sufficiently distinct one from the 

 other to be recognized Avitli comparative ease. 



Habits. All are eminently predatorj^, and our Enithares and Anisops are 



(1) Kirkaldy, Trans. Ent. Boc, 1897, p. 393. 



