1864.] 205 



Joint 1 lias attached to its lateral base a large, pale, fleshy branchia 

 (Fig. III. a) full of dai-k-colored interlacing vessels, above the origin of 

 which lies a much smaller flap-like piece (Fig. III. h) apparently de- 

 void of vessels. Joints 2 — 4 have on each side a very distinct spi- 

 racle, to exhibit which in Fig. Ill, the left branchia is removed. Joint 

 5 is twice as long as any of the others, which are subequal, and rises 

 upwards abruptly and almost vertically from its hind margin into a 

 transversely sinuate carina to receive the tip of the thoracic shield, 

 whence it is suddenly depressed downwards and forwards so as to leave 

 a cavity under the tip of the shield for the two branchiae to work in, 

 the shield being attached by membrane to the inferior portion of the 

 thorax, but only in front of the abdomen. Caudal setae three, equal in 

 length and diameter, multiarticulate and very finely pilose, the pilosity 

 indistinct except when the insect is alive and in the water, when it is 

 very obvious. Legs with the tarsi one-jointed and bearing a single 

 robust claw, the tibiae exceedingly short and connate with the tarsus. 

 No external wings. The % difiers from the 9 , not only in its much 

 larger eyes, but in being considerably slenderer. 



In the only known species belonging to this genus {B. obesa Say, 

 Walsh) the general color of the pupa is dull brown, variably marked 

 above and below with luteous. The legs are luteous with the tarsus, 

 tibia and femur each medially but irregularly fiisciate with brown, and 

 the femur with also a superior basal brown spot. Its general consist- 

 ence is pretty firm. 



The habits of this species are to frequent clear, rapidly-running riv- 

 ers, and to attach themselves in repose to the under surface of sub- 

 merged stones. Their food must consist almost exclusively of minute 

 particles of matter floating in the water, for of two which I bred to 

 the subimago state and two which partially attained that state — mak- 

 ing four in all — three lived for over five and one for six or seven days 

 in a glass vessel in clear but unfiltered cistern water, changed every 

 twenty-four hours and containing no solid substance whatever but a 

 piece of floating cork. I had originally placed a specimen in water 

 containing several dead aquatic larvaj and some jelly-like masses, pro- 

 bably confervge, which occurred in its natural station ; but on noticing 

 that it repeatedly crawled over such substances in an unconcerned man- 

 ner, I placed them all in simple water. It is singular that, neither in 



