140 ' THE CANADIAN ENTOMOLOGIST 



Bryozcans and fresh water sponges, together with the comb-horned f.sh fly, 

 Chatdiodes; the green may-fly, Baetis; Chironomid larvae; the stone fly Perla; 

 such caddis worms as Hydropsyche; and the Hydrophilid beetle, Hydrobiiis 

 glohosus. This m.ay-fly is also extremely localized in habitat for the im.agcs 

 were found for a distance of only about twenty feet and were abundant for only 

 about six feet. The immature forms were found in the stream opposite this 

 place of greatest abundance. At this point the stream bed breaks into gentle 

 riffles in which lives the mollusk, Anodonta footiana, in some numbers. Just 

 above the rififles the stream bed changes abruptly to soft, black ooze which is 

 filled with another mollusk, SpJicermm. 



The writer visited the stream on the 25th and 30th of June, hoping to find 

 the may-flies swarming, and if possible to observe mating and oviposition. 

 However, the season had been late and cold and there were no swarms, although 

 the nymphs were transforming; both subimagos and adults were clinging to the 

 herbage and shrubs along the stream. Although no egg masses could be found, 

 there were many of the small brown nymphs on the water-soaked wood, and 

 from some of these which were carried into the laboratory it was possible to 

 rear both sub-imagos and adults. 



Description of the Stages. 



Egg. 



A dissection of the ovaries of a female of this species showed the presence 

 of about six hundred eggs. The following description was made from material 

 thus obtained. The egg (PI. X, Fig. 9) is broadly ovate, .195 mm. long, by .11 

 mm. wide. The surface of the egg shell is laid off in numerous minute hexa- 

 gonal areas with depressed centres. The dissected material was translucent 

 whitish, and it was necessary to stain the shell to bring out the reticulation 

 clearly. 



Nymph. 



The fully grown nymph (PI. X, Fig. 8) is 7 mm. long with the three anal 

 setae 4 mm. long and subequal, and the antennae 1.7 mm. long. The body is 

 elongate, slender, flat below and slightly convex above. It is widest at the 

 meso thorax, while the pro thorax is slightly narrower than the head. The wing 

 pads project posteriorly over the margins of the first two segments of the abdo- 

 men. The abdomen is long and narrow, twice as long as the head and thorax 

 combined, widest at the sixth segment and with segments eight and nine pro- 

 duced posteriorly at each lateral margin into a triangular spine, while the caudal 

 margins of segments nine and ten bear a fringe of spines dorsally. The deeply 

 bifurcate abdominal gills are present on the lateral margins of segments one to 

 seven and are all approximately equal in length, with broad basal portion about 

 half as long as each of the slender terminal filaments. The body above is reddish 

 brown in colour and slightly lighter beneath. 



Mouth Parts of the Nymph. 

 The labrum (PI. X, Fig. 1) is larger than wide and rather deeply incised 

 medially, while on the under surface are a number of fine hairs which aid in 

 straining food particles from the water. The mandibles are very roughly 

 and irregularly triangular in shape, with the articulation and muscle attach- 

 ment occupying about half of the base and with a group of large, erect fangs 



