180 Journal New York Entomological Society. f'^'oi- ^^• 



pressions of the elytra (Figs ii and 12). At first I was led to suppose 

 that these insects secured their air supply as in the Dytiscidae, by 

 breaking the surface film with the tip of the abdomen and carrying an 

 air supply under the elvtra. I was led to this belief from seeing many 

 of them with an air bubble attached to the posterior end of the body. 

 But as the elytra are rather firmly held in place by the knob-like 

 structures it seemed doubtful if these beetles could open the tips of 

 the elytra and not at the same time allow the entrance of water. 



Fig. a. Lateral view of H. triopsis with wing cover removed to show method 



of respiration. 



However on close observation it was soon seen that the air supply 

 was carried under the broad coxal plates, at the posterior end of 

 which an air bubble is usually found. As the femora move back and 

 forth through this air supply I could not quite determine how the air 

 reached the spiracles. On examining beetles from which the elytra 

 were removed it was soon seen how the air supply became available. 

 In text figure (Fig. A) a beetle is shown in side view with one elytron 

 removed. Leading from the anterior end of the posterior coxa is seen 

 a narrow groove in the pleurum. This widens at first, then narrows 

 and finally divides into two branches. One branch passes backwards 

 and opens directly near the second abdominal spiracle. This air sup- 

 ply reaches all the abdominal spiracles. The other branch passes 

 forward and conveys an air supply into a large depression in which 

 are located the first abdominal and meta-thoracic spiracles. These 

 spiracles are much enlarged. The first abdominal spiracle is very 

 large, oval in outline and is almost closed by long, fine setse. 

 This condition of the enlargement of the first abdominal spiracles 

 is in marked contrast to that found in the Dytiscidse. The meso- 



