Sept., I9I2-] Matheson : Haliplid^ of North America. 179 



They prefer shallow pools although wherever there are sufficient 

 growths of Nitclla or Chara they may be found in the deeper parts. 

 In amongst the aquatic plants near the shores they may be found, 

 often very abundant and a single sweep of a small water-net may 

 bring up a dozen or so. It may also be noted that these beetles are 

 not found abundantly in all small pools but only here and there one 

 meets with them as one of the more dominant forms. I have found 

 them most abundant in spring fed pools which do not dry up during 

 the summer. In such pools some of the species are very abundant. 

 In a single pool I have taken the following species, listed according 

 to their relative abundance: H. ruftcoUis DeG., H. conncxiis Mathe- 

 son, P. edcniulns Lee, P. muticns Lee, H. triopsis Say, H. crihrarius 

 Lee. 



The adult Haliplids are poor swimmers and are never found in 

 the open water except when forced there. They live amongst the 

 plants bordering the shores and occupying the shallow waters. Here 

 they are found clinging to the stems of aquatic plants, swimming 

 short distances, or walking over the alg?e on which some species 

 feed. They swim by means of their legs, which are furnished with 

 long fringes of hairs. The tarsi of all the legs and the tibia of the 

 first and second pairs are provided with these fringes (Figs. 13, 14, 

 15). The fringes are long and supported by short, stiff setae (Fig. 

 14). The hind legs are the chief organs of locomotion and in swim- 

 ming move backwards with a slightly downward sweep. This is 

 brought about by the limiting action of the coxal plates which overlap 

 the first three to five abdominal segments (Figs. 11, 12). The hind 

 legs move alternately in swimming and so far as I can determine, all 

 the legs move in the same manner as they do in walking. They swim 

 but slowly. On land they walk or run with considerable ease and 

 agility, raising the body clear from the surface and placing the weight 

 on the tarsi of all the legs. I have never found these beetles at elec- 

 tric lights nor have I seen them use their wings in flight, though they 

 probably do fly. 



Their method of respiration is rather unique and nothing like 

 it has been described so far as I know. The elytra are firmly held 

 in place not only by the groovings in the pleura but also by the 

 knoblike structures on the anterior outer ends of the posterior coxae 

 (Fig. 12). These knob-like structures fit closely into socket-like de- 



