ODONATA OF THE VICINITY OF GO HOME BAY 81 



SESSIONAL PAPER No. 39b 



Dorsal surface rather strongly convex, dorsal hooks present on 1-9, those 

 of the basal segment slender, nearly erect and slightly hooked, becoming gi'adually 

 broader and lower caudad, and, on 7-9 reduced to scarcely more than a short ridge. 

 Superior appendages triangular, equilateral, very slightly shorter than the some- 

 what divergent inferior appendages and somewhat longer than the lateral 

 appendages. 



Colour yellowish or orange brown, variegated with dark brown. Head dark 

 brown above, generally somewhat paler in the centre and on the frontal ridge. 

 Thorax and wing-cases vaiiegated with pale and daik markings; femora and tibiae 

 with two pale rings, a median and anteapical. Abdomen yellowish biown, more 

 or less distinctly blotched with darker brown, especially on the dorsal hooks, 

 the lateial margins and spines and the dorso-lateral scars. 



Measurements : Length of body 22-24 • 5 ; hind wing, 6-7 ; hind femur 5-5 • 6 ; 

 width of head 6*5; width of abdomen 9-10; mentum of labium 4. 



The nymph of this species shows the following differences from that of N. 

 obsoleta, two exuviae of which I have from Lake Hopatkong, Pa., received from 

 Professor P. P. Calvert. 



Somewhat larger, more elongate and less depressed ; eyes somewhat less prom- 

 inent, mentum of labium a little longer and more nan owed at base, middle and 

 hind legs somewhat less widely separated at their bases; abdomen narrower, the 

 sides less strongly curved on the middle segments; lateral spines on segment 9 

 much shorter than those of obsoleta, in which they are fully as long as the segment 

 and extend far beyond the tips of the appendages ; dorsal hooks also less developed 

 than in obsoleta, in which they form quite prominent tubercles on segs. 7-9. 

 (PL IV, Figs. 16-19). 



Besides the full-grown nymph we have taken specimens of two, earlier instars, 

 measuring 8 and 18 mm. in length respectively. Judging from the great difference 

 in size between these three instars, it would seem probable that the larval period 

 must be at least two, if not three, years long. In the youngest instar the lateral 

 spines are relatively much longer than in the older ones. 



The nymphs of A^. yamaskanensis cling to the undersides of boulders along 

 the more exposed shores. As the exuviae are most commonly found on steep rocky 

 shores, rising almost perpendicularly from the water, (PI. V, Fig. 27) it would seem 

 that the nymphs prefer water of considerable depth, i.e., 8 or 10 feet or more, 

 but we have often taken nymphs of several stages in water less than two feet deep. 

 They occur along the outer coast as well as in the river, in fact wherever the water 

 is kept more or less constantly in motion. They are common in the vicinity of 

 falls and rapids. One exuvia was found on a log overlying the falls at Muskoka 

 Mills. The nymph had evidently crawled out of a comparatively quiet spot close 

 to the swiftest part of the fall, where the water was thoroughly aerated. 



The nymphs are associated with the nymphs of mayflies of the genera Hep- 

 tagenia, Blasturus and Baetis and of the damsel-fly Argia moesta putrida, upon 

 which they probably feed. I found one at the "Narrows" of the Go Home River, 

 supporting a growth of a Polyzoan, Plumatella sp. 



In 1912 adults emerged in the laboratory from Jime 23 to July 8. Their season 

 39&— 6 II 



