May, 1921.] 



The Canadian Field-Naturalist. 



89 



adian localities given on the following 

 pages have been verified by Professor A. 

 S. Pearse, of the University of Wisconsin. 



Canadian ''dam-shrimps" were first 

 described in 1862 by W. Baird from spe- 

 cimens {Limnetis gouldii) collected by Ch. 

 (rould in June 1857 at St. Anns, Montreal, 

 P.Q., and from specimens (Esthcria cald- 

 welli) collected by W. Caldwell in Lake 

 Winnipeg, Man. They are represented 

 upon this continent by three families (sub- 

 families) ; the Limnetidae, Limnadiidae 

 and Estheriidae, the two last families being 

 often united l)y autliors. The first family 

 is easily distinguislied from the two others 

 by the milky colored shell being more or 

 less spherical and Vv'ith lines of growth, and 

 the head cannot be retracted into it. In 

 these characters the family reminds one 

 strongly of the Cladocera, especially the 

 family Lynecidae, though the clam-shrimps 

 do not possess the huge claw-foot of these 

 Cladocera. Only one genus (Limnetis, es- 

 tablished by Loven in 1845) belonging to 

 this family of clam-shrimps occurs in 

 North America, but it is represented by 

 four species of which three are known onl}^ 

 from the United States (L. mucronatus 

 occurs in Montana), but one {L. gouldii 

 Baird) also in Canada. This latter spe- 

 cies is rather liardy and easy to keep in an 

 a(piarium; the eggs are found under the 

 back of the sliell of the female in the spring 

 and early summer (May- July), according 

 to Packard. It has been recorded from 

 New Hampshire, Massachusetts, Rhode Is- 

 land, New York and Illinois; from Can- 

 ada I have l>efore me specimens from the 

 following localities, arranged from east 

 to west : — 



About two dozen specimens from a wood 

 beyond Montreal West, P.Q., June 17, 

 1917, A. Willey, coll. (sent to me from 

 McGill Museum). 



Many specimens (the smaller ones red- 

 dish, the larger ones, some of which are 

 egg-bearing females, yellow-green * collect- 

 ed by myself in a ditch-canal left by the 

 overflow of the Ottawa River on the fields 

 a little east of Gatineau Point, P.Q., June 

 14, 1919. When I visited this place again 

 on October 19 of the "same year the ditch 

 was completely dried up, being filled with 



* Baird describes his specimens, wliich were 

 3x3 mm. long, as having a pale fleshy-yellow- 

 ish color, with black eyes. 



Carex and much other vegetation ; no clam- 

 shrimps were of course observed on that 

 occasion. 



On April 18 and May 30, 1920, I again 

 visited the same ditch; but as the water- 

 level of the Ottawa River this year was 

 (even at its maximum) much lower than 

 in 1919, there was no connection between 

 the river and the ditch. The latter had 

 very little water left, merely small holes 

 which contained only some aquatic mol- 

 luscs, insects, tadpoles, and the Isopod 

 Asellvs communis. The farmer who owned 

 the field upon which the ditch was situated 

 had ploughed it up and partly filled in 

 the diteli, so the latter will probably never 

 again contain any "clam-shrimps." 



On May 2nd, 1921, I collected a number 

 of immature (II/2 to 2 cm. long) speci- 

 mens of this species, in a fairly large and 

 deep pond on a field on the hills at Tenaga, 

 west side of Gatineau River, P.Q. They 

 had a vivid orange or red-brown colour, 

 and were easy to catch as they were swim- 

 ming slowly ("suspended") in the water, 

 or attacliing themselves to plants. They 

 occurred in great numbers, together with 

 Cladocera, Ostracoda, and the fairy-shrimp, 

 Euhraiichipus gelidus, etc. At the end of 

 May neither fairy-shrimps nor Conchos- 

 traca wore to be found in this pond. 



Mr. W. S. Odell, of Ottawa, tells me 

 that about a dozen years ago he secured 

 many of these clam-shrimps in a pool on 

 the fields at WychAvood (near Aylmer), P. 

 Q., and that he secured more in the same 

 place during the succeeding years (in 

 May). When I visited this pool on May 

 15, 1921, it Avas quite dried up, and fur- 

 thermore used as a dump for rubbish, so 

 that it probably contains no more Crus- 

 tacea. Mr. Odell also secured them in 

 pools alongside the railway-track near 

 Hurdniau's Bridge (Rideau River ") about 

 a dozen years ago; but for several years 

 their habitat there has been destroyed. 

 Furtlieimore, for several years Mr. Odell 

 has observed them in tlie pools left by the 

 overflow (in the spring) of the Rideau 

 River on a pasture at Billings Bridge. Ot- 

 tawa South, near the brick-yard; and he 

 showed me some he had collected there, to- 

 gether with the fairy-shrimps Euhrnnchi- 

 pus r/(Iidus of both sexes, on the first week 

 of May. 1921. A week later he and I 

 visited the place, but did not succeed in 

 finding a single fairy-shrimp, tiiough the 



