80 MARINE AND FISHERIES 



5 GEORGE v., A. 1915 



with its exuvia in a crevice of a steep rocky bank. It proved to be N. yamask- 

 anensis. Subsequently a number of others were found with their exuviae on 

 Station Island. Generally they were found between 7 and 8 a.m., but a few 

 were taken late in the evening. Early morning appears to be the usual time 

 for transformation. For some days adults could only be obtained in this way, 

 but they were at last discovered by Mr. Eraser flying about the island at dusk. 

 It was soon ascertained that their time of flight is limited to about half an hour 

 a day, commencing soon after sundown (a little after 8 p.m.), and continuing 

 until shortly after 8.30, after which they retire to the shelter of the trees. It is 

 thus nearly coincident with that of the mayflies, Ephemera, Hexagenia, Heptagenia, 

 etc., upon which they appear to feed exclusively. 



During this short time of flight they are extremely active. They dash about 

 erratically over the rocks among the swarms of mayflies and when one of these 

 is captured they retire with their prey to a neighbouring tree to consume it in 

 peace. 



The majority of the individuals thus engaged are females. The males will 

 be found at the same time flying over and within a few inches of the water close 

 to the shore which they follow very closely. They fly back and forth in a regular 

 beat and with extraordinary swiftness. During these flights the males apparently 

 do not feed, but seem to be on the watch for females, for now and then a male i» 

 seen to pounce upon a female, the pair then sailing off over the water or up into 

 the trees, where copulation takes place at rest. Except when thus seized by the 

 males, no females were observed close to the water though plenty of them could 

 always be seen flying over the rocks nearby. 



Nymph: (Fig. 15-17) short-legged and of stouter build than most Corduliines. 



Head broadly convex above and on the sides, eyes not very prominent, frontal 

 ridge with a scurfy pubescence, the anterior margin convexly curved, hind angles 

 of head prominent, distance between them a little greater than half the greatest 

 width of the head; hind margin distinctly excavate. 



Labium extending very slightly behind the bases of the front legs; mentum 

 somewhat broader at the distal margin than long, the middle lobe somewhat ab- 

 ruptly deflexed, bluntly obtusangulate; mental setse 9-11, the innermost 3 or 4 

 much smaller than the others; lateral lobes triangular, their distal margins pro- 

 duced into seven semi-elliptical teeth ; lateral setae 6 ; movable hooks very slightly 

 arcuate. 



Marginal ridge of pronotum produced on each side behind the posterior angles 

 of the head as a prominent process which is somewhat smaller than the very prom- 

 inent supra-coxal processes. 



Legs short, the length of the hind femora being slightly less than the width 

 of the head. 



Abdomen ovate, its greatest breadth, at segs. 6 or 7, slightly greater than 

 two-thirds of its length; curve of the lateral margins somewhat stronger in the 

 distal than in the proximal half; lateral spines on 8 and 9, in each case about one- 

 third to one half as long as the corresponding segment, those on 8 strongly diver- 

 gent, on 9 parallel and extending caudad scarcely or not at all beyond the tips 

 of the appendages. 



