GEORGIAN BAY EPHEMERIDM 119 



SESSIONAL PAPER No. 39b 



Face pale, slightly tinged with brown along the carina. Dark brown on dorsal 

 surface of head between eyes. Pronotum dark brown; mesonotum lighter; a dark 

 brown line on each side of prothorax, extending forward from base of fore wing; 

 other dark brown marks at bases of wings and legs. Dorsal surface of abdomen 

 dark brown, somewhat lighter laterally toward anterior margin. Ventral surface 

 light in colour. Genitalia of usual Ecdyurus type. Legs light in colour, dark 

 at joints. Tarsi of fore legs in order of increasing lengths 1, 5, 4 (3 and 2) equal. 

 Wings with longitudinal and cross veins brown, and very slightly darkened in 

 apical costal region. 



Nymph: 



Measurements: Body 12 mm.; setae 15. 



Head brown with a colourless area on each side from eye to lateral margin 

 of head and 3 light dots between eyes; slightly fringed with hairs along anterior 

 margin. Pronotum somewhat lighter in colour than head, colourless areas along 

 anterior and lateral margins and a light area about the middle of each half of 

 pronotum. Mesonotum darker with numerous light spots. Each segment of 

 abdomen brown; 1-8 have 6 light spots; on segments 4-8 the 2 near the median 

 line are fused, forming a large, almost rectangular spot; segment 9 with only 4 

 light spots; segment 10 entirely brown. Gills comparatively small; lamellae 

 oval. Setse of about equal size, with each 2 alternate segments brown; sparsely 

 fringed at joints; outer margins of lateral ones not fringed. Femora stout and 

 flattened, brown in colour; lighter at distal and proximal ends and 2 or 3 irregular 

 light areas toward middle; covered with minute spines and fringed along posterior 

 margin with hairs. Tibise alternately light and dark banded, fringed along both 

 anterior and posterior margins. Tarsi brown with proximal tips colourless. 

 Ungues double on each leg; the large one well curved; the other small and lateral 

 to the large one. 



The nymphs were collected along the very stony shores of islands three and 

 four miles out in the open bay, from June 23 to July 6. Imagos were reared on 

 July 2 and a few captured June 27th. 



In the key to the genera of Mayflies of North America by Professor Needham 

 in Bulletin 86, New York State Museum, there is a slight error in the separation 

 of the genera Ecdyurus and Heptagenia. In Ecdyurus the basal segment of the 

 male fore tarsus is shorter not longer than the fifth segment and the second and third 

 segments of equal lengths. In Heptagenia the basal segment of male fore tarsus 

 is longer than the fifth segment and the second and third segments may be equal 

 or unequal. 



Baetisca obesa Walsh. 



This very interesting nymph was taken in only two localities. The one was 

 along the north east shore of Giant's Tomb Island. This shore is quite sandy 

 with numerous small stones and deepens very gradually. The nymphs were abun- 

 dant here May 26, clinging to the stones in water from 3 to 15 inches deep. Some 



