D2 THOMAS SAY FOUNDATION 
of compound gill tufts distributed as follows: two pairs at the 
outer base of the prothoracic legs just underneath the lateral 
shields of the pronotum; one pair each in a similar position on 
the meso- and metathorax; one pair each on the outer conjune- 
tivae between the pro- and mesosternum, and between the meso- 
and metasternum ; and one pair just back of the base of the meta- 
thoracic legs. Anal gills absent. 
The sexes are not readily distinguished; however, in the ma- 
turer nymphs the females may be recognized by the small median 
notch on the posterior margin of the eighth abdominal sternite, 
and often the abdomen is seen to be distended with dark eggs. 
Mouth parts: labrum about three times as wide as long, with 
a fringe of long hairs on the anterior margin; epipharynx broadly 
rounded when fully extended, and closely beset with short spines. 
Mandibles triangular and rather slender, somewhat asymmetrical, 
each with five unequal sharp teeth, followed by a fringe of long 
hairs. Maxillae: lacinia long and slender and terminating in two 
long sharp teeth; following these teeth, a fringe of long, stout 
hairs. Galea slender, two-segmented, tipped with papillae and 
a few long hairs, and not reaching quite to the tip of the lacinia; 
maxillary palpus slender and extending somewhat beyond the 
tip of the lacinia. 
Labium wider than long; submentum very large, mentum a 
narrow transverse band; glossae very short and broadly rounded ; 
paraglossae large, somewhat pear-shaped and directed inward; 
both glossae and paraglossae hairy and at the tips closely beset 
with papillae. Hypopharynx thickly covered with short spinules. 
The nymphs of this species are common in the larger swift- 
water streams with stony bottoms. They restrict themselves 
largely to the underside of stones and are able to maintain a 
foothold in very swift currents of water. They are voracious 
feeders, feeding on mayfly nymphs, midges, blackfly larvae and 
pupae, and even on stonefly nymphs. Examination of stomach 
contents also reveals the presence of many diatoms which, how- 
ever, are probably ingested incidentally while feeding on animal 
prey. Miss Smith (52) found that in the younger stages the 
nymphs of this species apparently ingested a greater number of 
diatoms than they did as they grew larger, and this would in- 
dicate that during the early stages diatoms form part of the 
preferred diet of these nymphs. 
No one has worked out the complete life history of this species, 
but it apparently requires three years to complete its life cycle. 
