HUNGERFORD: AQUATIC HEMIPTERA. 199 
KEY TO AMBRYSUS—continued. 
BB. Head very sensibly narrower, including the eyes, less than 
half the width of the pronotum behind. Pronotum with a 
slight depression, sometimes very superficial, wrinkled trans- 
versely on the middle of the anterior border. 
C. Coloration darker, segments of connexivum darkened 
with posterior angle a little prominent. A. pudicus. 
CC. Coloration lighter, segments of connexivum not as above. 
A. circumcinctus. 
AA. Pronotum densely punctate, especially laterally. 
B. Size small, below 8 mm. Median depression of the anterior 
margin of the pronotum feeble, transversely wrinkled. 
Color “claire.” Width of the head, including eyes, a little 
less than half the width of the pronotum behind. Eyes con- 
verging in front. Length, 7.2 mm.; width, 4.5 mm. 
A. californicus. 
BB. Size larger, above 9 mm. in length. 
C. Anterior margin of pronotum very visibly ‘“rebordé” 
(with a visible ledge) behind the eyes; depression of the 
middle of the anterior margin transversely wrinkled and 
punctate between the wrinkles; interocular portion of the 
head narrowed in front; head with a very feeble longi- 
tudinal depression forming a median furrow, plainer 
behind. Length, 11.8 mm; width, 6.7 mm. 
A. melanopterus. 
CC. Anterior margin of pronotum not or slightly visibly 
ledged (bordered) and then only in the middle. 
D. Anterior angles of pronotum very prominent, 
sharp. 
E. Average size larger (9.3 to 10.6 mm.) ; lateral 
sides of pronotum more dilated and more 
strongly arcuate without, dilation of embol- 
ium more pronounced. Coloration pale. 
A. mormon. 
EE. Average size smaller (8.6 to 10 mm.); lat- 
eral sides of pronotum less dilated and less 
strongly arcuate without; dilation of embol- 
ium less pronounced. Coloration deeper. 
A. heidemanni. 
DD. Anterior angles of pronotum less prominent, almost 
right angles, scarcely pointed. 
E. Head narrow, as long as the width of the in- 
terocular space behind; length of the head 
and pronotum together a little greater than 
half the greatest width of the pronotum. 
A. puncticollis. 
EE. Head wide, length of the head and pronotum 
together equal to or a little less than half the 
greatest width of the pronotum. Pronotum 
