Octcber, 1920.] 



The Canadian Field-Naturalist 



129 



One full-grown female with pink eqg.-. (4) 10 

 specimens, pool near Gatineau Point, P.Q., May 

 13, 1917, (3 of the females wiih eggs). (5) Sev- 

 eral specimens (all sizes; full grown f.>male with 

 eggs), from pool at Catfish Bay, Hull, P.Q., N4a}' 

 I6lh, 1920. (6) Pool in woods at Rcckcliffe, 

 Ont., May 24, 1919, one full grown female with 

 newborn young in the brood-pouch. (7) Bight in 

 Ottawa River, Hull Park, P.Q., July 6, 1919; un- 

 der stones, several specimens mostly full grown fe- 

 males with ripe eggs and young in brood-pouch. 

 Twc young specimens from Montreal West, Que., 

 Oct. 19, 1918, A. Willey, coll. 



Some interesting facts about the life history of 

 this species will be gleaned from the above new 

 records. There thus seems to be at least two 

 broods each summer, one in May, the other in 

 July, and probably also one in September, in the 

 surroundings of Ottawa. Its frequent occurrence 

 in temporary pools, bights or streams is also note- 

 worthy, and it reminds one of what is known about 

 the phyllopods. When full grown its size is about 

 double that of Hyalella, but only half of that of 

 Cammarus. It is not nearly so frequent as these 

 two species (H. f(nicl(erbocf(eri, C. limnaeus), 

 though at certain places where it is found it may be 

 common enough, (see above under (2), Deschenes). 



Though the color of freshwater amphipods is to 

 a large extent caused by the immediate surroundings 

 and their food, the color of Eucrangon^x gracilis 

 is like that of green glass, changing to yellowish or 

 orange in the females at the time the eggs ripen. 

 Its geographical distribution has already been re- 

 ferred to. 



Of the genus Cammarus we have two species in 

 Canada, of which one (G. fasciatus) hardly occurs 

 here at all (outside of the Great Lakes) ; but the 

 other (C. limnaeus) is found over the whole width 

 and breadth of the mainland part of the Dominion 

 and Alaska. C. fasciatus is known from Niagara 

 River and Lakes Superior and Michigan, also from 

 Georgian Bay. In the United States it is found 

 from Maine to Wisconsin. It is common enough 

 where it occurs according to various authors (Hunts- 

 man, Shoemaker) but I have never observed or col- 

 lected it myself. It resembles very much the other, 

 more widely distributed species G. limnaeus, and 

 the young of the two species are very difficult to 

 separate. 



Cammarus limnaeus is differentiated from its near 

 relative C. fasciatus by the fact that the long hairs 

 upon the terminal joint of the outer ramus of the 

 uropods, are plumose, and not simple; a character 

 only to be ascertained by the aid of the microscope 

 and with net too young or imperfect specimens. It 

 is interesting to note, that while G. fasciatus, as 

 mentioned above has only a limited range in Can- 



ada, C. limnaeus is distributed over the whole width 

 and breadth of the Dominion'^ from the American 

 border to the Arctic ocean, the reverse is the case 

 as one goes south on this continent. Mr. Shoe- 

 maker tells me, that at Washington, D.C., G. fasci- 

 atus IS far more common than G. limnaeus. The 

 latter species is found in larger pools in lakes and 

 in streams, the younger individuals having the habit 

 of hiding under stones and vegetation (moss, algae, 

 etc.), the older ones swimming around freely. As 

 I observed them in the arctic they seem to be found 

 only in lakes which owing to their depth do not 

 freeze to the bottom during the winter, or in creeks 

 (rivers) which v/ere open (or partly so) all the 

 year round. Where they occur in temporary pools 

 and streams at more southern latitudes it can, ac- 

 cording to my own observations (Ottawa and St. 

 Lawrence rivers), mostly be e.xplained by the fact 

 that these temporary bodies of water were in con- 

 nection with the rivers or large lakes earlier in the 

 season, and the amphipods, therefore, probably 

 migrated into them at that time. In the arctic I 

 found them during the period October to June in- 

 clusive, when the lakes had thick ice and generally 

 just below the ice. I suppose their main food then 

 IS the many Entomostraca (copepods) swarming 

 here. That they live a pelagic life is also indicated 

 by the fact that the many trout caught here had 

 their stomachs filled with them at that period. When 

 the lakes are free of ice or when the ice is thin 

 (July to September inclusive) the amphipods lit- 

 erally swarm in shallow water along the margin of 

 the lake, and seem to find their food more among 

 the many plants (moss, algae) on the stones in such 

 situations. The detailed data for the specimens of 

 this species collected on the Arctic coast (Sadle- 

 rochit River, Alaska, Herschel Osland, Yukon 

 Territory, Bernard Harbour, Northwest Territories) 

 have been recorded on p. 16 in Shoemaker's re- 

 port. Mr. Shoemaker tells me, that the specimens 

 from the warm spring creek tributary to Sadlerochit 

 River, and which lived in water of a temperature 

 from 40 to above 60 F., cannot be distinguished 

 from those from the other arctic localities except 

 perhaps by their average, smaller size. 



Curiously enough, egg-bearing females of this 

 very common species, which I have observed so 

 often at many localities in Canada are far less 

 frequently^ met with than is the case with the more 

 rare Eucrangonyx gracilis ; it is perhaps because the 



Huntsman says (I.e.) p. 151 tliat tlijs species is 

 much less abundant in the waters examined than 

 G. fasciatus: but he did not tlien Ivnow of the 

 many records of G. limnaeus from various parts of 

 the Dominion now secured. 



tTwo of the specimens collected in Whitefish 

 Creek, Lake Simcoe, Ont., June 17, 1917, by E. M. 

 Walker were egg-bearing females. 



