164 THE UNIVERSITY SCIENCE BULLETIN. 



versely elongate, somewhat flattened on the inner margin, projecting 

 beyond the expanded anterior portion of the prothorax. Antennae are still 

 two-jointed, the basal joint extending into a process, nearly as stout as the 

 terminal joint, and about three-fifths as long. The suture between the 

 joints is very faint. The joints are now abundantly furnished with the 

 tactile spines, which reach full development in the adult. Prothorax 

 widened anteriorly by the sockets of the anterior pedes, gradually con- 

 stricted towards middle, and expanding again basally, but not quite as 

 broad as the anterior portion ; excavate for the insertion of the head and 

 truncate posteriorly. Prosternum not sulcate, deeply excavate posteriorly. 

 Mesothorax with long narrow wing-pads of the hemelytra, pointed pos- 

 teriorly in the middle. Metathorax concealed. First abdominal segment • 

 showing as a ring between the wing-pads of the posterior alae, which 

 barely attain the extremity of the pads of the hemelytra. A straight 

 suture marks off this segment from the next. The abdomen is more 

 than twice the length of the thorax, the segment following the thorax 

 slightly constricted. The sides of the abdomen are folded over itself, and 

 are furnished with fringing hairs. There is an indentation in the edge 

 at each segment that bears the thickening of the formative pseudo- 

 stigmata. The abdomen has only six apparent segments and the siphon 

 or air-tube. The false stigmata show in segments three to five, dorsally, 

 as thickenings of the integument, darker than the surrounding skin. The 

 siphon is jointed to the sixth segment, and freely movable. The abdomen 

 is keeled beneath, the keel bearing a fringe of short hairs on each side, 

 which meet those of the inflexed abdominal margin. The legs approach 

 more closely to the adult. The second so-called tooth or prominence in 

 the first pair is quite evident. The true tooth is large and triangular, 

 and the clawless tarsus rests against it when the tibia is folded on the 

 femur. The second and third pair are slender, ciliate, with globose coxas; 

 the tarsus of the second pair does not quite reach and the second goes 

 slightly beyond the end of the siphon. Both these are one-jointed, and 

 armed with prominent curved double claws. 



"Size: Long., 44.4 mm. (from tip of rostrum to tip of siphon); lat., 

 2.9 mm. (at the thorax, but not at wing-pads). Siphon, long., 12.3 mm. 



"Colour: More or less luteous of varying degrees, without any special 

 pattern. The legs, which in the preceding instars are banded, are ap- 

 parently unicolorus in this. This, however, may be the peculiarity of the 

 two individuals from which this description has been drawn up. The 

 eyes are black and shining." 



Family NOTONECTID^ Leach 1815. 



Leach, Brewster's Edinbg. Encyc, IX, p. 124. 



A. Taxonomy of Notonectid^. 



Family Characteristics. Perfectly aquatic forms, differing from all 

 others in the persistent habit of swimming on their backs. They are 

 much deeper bodied than other Heteroptei'a which live in the water, and 

 while being oval in form with the apex of the wing-covers conical, have 

 the convexity of the surface above. Their eyes are large, reniform, twice 

 sinuated on the outer side, and project a little way over the front margin 

 of the prothorax. Ocelli are absent. Antennas 4-segmented, shorter than 

 the head and partly concealed in depressions between the head and 

 thorax. Rostrum 3- or 4-segmented. Hind limbs fringed for swimming 

 (sometimes not conspicuous in museum specimens of Plea.) Tarsi 2- 

 segmented (male of Anisops has one segmented tarsi on front limb.) 

 Two tarsal claws present in all, but inconspicuous in the hind limbs of 



