HUNGERFORD: AQUATIC HEMIPTERA. 227 



stripe by a spot of dark pigment. On the hind margin of the head there 

 are two spots, visible only when the head is bent forward. The caudal 

 margin of prothorax is margined with a dark band. Base of meso- 

 thoracic wing-pads marked with dark irregular spot. Hind margin 

 with arcuate band of color and two faint arcuate bands upoij the disc. 

 The metathorax is marked with pairs of irregular smoky spots as de- 

 lineated. Abdomen markings as in former instars. 



Structural Peculiarities. The wing-pads are now well marked and ex- 

 tend back slightly more than half the length of the margin of the meso- 

 and metathorax taken together. Tibia as well as tarsus of hind leg with 

 swimming fringes. Claws of hind tarsus now not more than one-fifth 

 the length of the tarsus. The claws present the peculiar incised ap- 

 pearances as before. The middle femur is longer than the tarsus and 

 tibia together. The marginal series of spines as delineated. 



Fourth Instar. 

 Size. Length, 3.072 mm.; width of body, 1.43 mm.; width of head, 1.19 

 mm.; distance between eyes, 0.39 mm. 



Shape. About as in third instar. 



Color. The ground color is pale fuscous with darker markings ranging 

 from smoky to reddish-brown. The face bears the pair of smoky rec- 

 tangular blotches noted in former instars. From above the vertex is 

 marked by three longitudinal stripes. The median one is slender and the 

 lateral ones irregular in outline. The thorax is marked as delineated in 

 the plate. The darker part reddish-brown, the scroll on the metathorax 

 being the most characteristic. The abdomen is crossed by reddish-brown 

 transverse bands, which at the margin of abdomen blend into triangular 

 smoky spots. The body of abdomen is further marked by two longitudinal 

 broken bands of fairly dark pigment, one either side of the dorsal glands. 

 These converge from the base of the abdomen to the caudal end, where 

 they meet. The caudal margin of hind tarsus bears a roughly triangular 

 dark blotch, its apex reaching in some cases two-thirds of the distance to 

 the cephalic margin. 



Structural Peculiarities. The wing-pads now extend more than two- 

 thirds the length of the meso- and metathorax. The hind limbs are now 

 well adapted for swimming, the hind tarsus being broad and flat, and the 

 swimming fringe very complete. The claws are reduced now to perhaps 

 one-seventh of the length of the tarsus, and are less conspicuous than 

 formerly. There is a small tibial comb of six short spines at distal end 

 of the tibia. This structure is present but inconspicuous in the previous 

 instar. The marginal series of spines as delineated. 



Fifth Instar. 



Size. Length, 3.9 mm.; width of body, 1.7 mm.; width of head, 1.3 mm.; 

 distance between eyes, 0.39 mm. 



Shape. As before, save that the length is greater in proportion to 

 width. 



Color. Color pattern substantially as in previous instar. The long 

 wing-pads, however, are darker. 



