46 



The Canadian Field-Naturalist. 



[Vol. XXV. 



be remembered that the eggs ^ are carried 

 a much longer time by the mother animals 

 and develop more slowly than wit,h 

 the fairy-shrimps. Judging from the arc- 

 tic form {Lepidurus arcticus) both sexes 

 apparently live more than one year and 

 probably hibernate in sufficiently deep 

 ponds or lakes, supposing, of course, that 

 they do not freeze into the ice, are not 

 killed by the drying-up of the pond, or 

 that their life-cycle is not completed. The 

 larvae apparently are too few and frail to 

 keep the numbers up alone from year to 

 year; this, coupled with the comparatively 

 (i.e. compared with the fairy-shrimps) 

 slow growth of the young individuals and 

 the large size they have to attain, makes a 

 normal age of several years a necessity, 

 at least for the females. 



While, so far as we know, the arctic form 

 occurs year after year, the same is not the 

 case with the more southern species. In 

 some years the latter are entirely absent, 

 or only females occur, and in this respect 

 they are not unlike the "clam-shrimps". 

 To a still larger extent than is the case 

 with the "fairy-shrimps" the "tadpole- 

 shrimps" and "clam-shrimps" are very 

 erratic in their occurrence, especially out- 

 side the arctic; smaller ponds and pools 

 may be teeming with them, while they are 

 not found in others, nor in lakes close by; 

 again they may be plentiful only at a cer- 

 tain time of the year. 



Of the tadpole-shrimps only two genera 

 are known, both occurring in the new as 

 well as in the old world. They are easily 

 separated by the spatulate or triangular 

 outgrowth from the telson present in the 

 one (Lepidurus), but absent in the other 

 genus (Apus). 



To Lepidurus belong about half a dozen 

 species, to Apus about a dozen, of which 

 four of each genus have so far been re- 

 corded from this continent. It is interest- 

 ing that no Apodida have so far been found 

 east of a line from Kin^g William Land 

 south to Manitoba and the middle States, 

 though the Arctic species is apparently 

 circumpolar and has been recorded from 

 Labrador and Greenland. 



Of the four species of Lepidurus two 

 have so far only been recorded from Colo- 



2 At least the "winter-eggs." 



rado and California and are likely to occur 

 neither in Canada nor Alaska. A third 

 species (L. couesii) was originally des- 

 cribed by Packard from Utah and Mon- 

 tana and has since been collected in three 

 of the western provinces of Canada (Man- 

 itoba, Saskatchewan and Alberta) ; it 

 probably occurs also in British Columbia. 

 Its carapace is large, so that only five 

 "tail" segments and the spatulate telson 

 are uncovered. Packard's specimens (botli 

 sexes) from Montana were taken in the 

 first week of July, 1874, and had an aver- 

 age length of about 2cm. (exclusive of the 

 cercopod-stylets). The Alberta specimen 

 (see below) is nearly of the same size (it 

 was dried up when I found it) as a spe- 

 cimen (female) about 3 cm. long from 

 Dufton, Sask., now in the Royal Ontario 

 Museum, Toronto; the latter was collect- 

 ed by a university student on June 20, 

 1913. 



Prof. O'Donoghue, of the University of 

 Manitoba, writes me (June, 1920) that 

 he has recently collected this species (L. 

 couesii) near Winnipeg, where it "is ex- 

 tremely common in the ditches on the west 

 side of the south end of Lake Winnipeg". 

 He has promised to send me specimens of 

 it. 



From Prof. A. G. Huntsman, of Tor- 

 onto, I have recently received a number 

 of specimens of the same species from one 

 to two cm. in length. He collected them 

 on June 11, 1920 in sloughs three miles 

 north-east of Medicine Hat, Alta., where 

 they occurred together with the fairy- 

 shrimp Strepfocephalus coloradensis (see 

 page 29), and clam-shrimps (see later). 



We have in the museum here in Ottawa 

 a specimen of the same species apparently 

 collected by J. B. Tyrrell in southern Al- 

 berta or British Columbia in the eighties. 

 I found it among a number of other in- 

 vertebrates from land and freshwater col- 

 lected by Tyrrell at that time, but there 

 was no date with it, and Mr. Tyrrell was 

 not able to recollect the locality or date 

 when I sent him the specimen. Beyond 

 what is given here nothing is known as 

 to the northern limit for this species; ap- 

 parently, however, it is not found in the 

 Yukon and the Northwest Territories, nor 

 in Alaska, though it may occur in the most 

 sonthem part of the last-named territory. 



