190 Journal New York Entomological Society. t^'o'- ^^ 



is found in the way the larvae of Pcltodytcs secure an air supply. 

 In Haliplus there are present two thoracic and seven abdominal 

 spiracles. In Pcltodytcs no spiracles are to be found till the pupal 

 stage is reached. The larvae as pointed out possess many, long, 

 jointed spines. As shown by Schiodte these spines contain tracheae 

 which undoubtedly function for the securing of an air supply from 

 the oxygen dissolved in the water. Fig. 30 shows a part of a segment 

 containing a large trachea (each spine contains but a single large 

 trachea) with numerous tracheoles arising from it. Fig. 31 shows 

 the termination of a trachea in three tracheoles. It is by means of 

 these tracheated spines that the larvae of Pcltodytcs secure an air 

 supply. 



In conclusion I wish to thank Professors A. D. MacGillivray and 

 J. Chester Bradley for criticism and advice in the preparation of the 

 systematic part of this paper and Professor J. G. Needham for his 

 aid in the working out of the life-histories. 



Summary. 



The adults. — (i) The commoner species of Haliplus and Pclto- 

 dytcs are widely distributed and are at times locally abundant in 

 spring fed pools. 



(2) They feed almost exclusively on filamentous algae, particu- 

 larly Nitclla and Chara. 



(3) They are poor swimmers, the hind legs being the chief organs 

 of locomotion. The legs are furnished with fringes of long hairs. 



(4) They secure their air supply by w-ay of the posterior coxal 

 plates and the grooves in the pleura. The metathoracic and first 

 abdominal spiracles are enlarged. 



(5) Mating begins in the early spring and the eggs are deposited 

 during the latter part of April, May and June. The species of 

 Pcltodytcs attach their eggs to aquatic plants mainly Nitclla and 

 Chara, while Haliplus (H. ruficollis) places its eggs within the dead 

 cells of Nitclla. 



The Larvcc. — (6) The larvae have only three instars (two molts). 

 They apparently feed exclusively on filamentous algae (conjugatae). 



(7) The larval mouth-parts are adapted for feeding on algae. 

 The first pair of legs are modified into organs for grasping and 

 handling alsral filaments. 



