. The Canadian field-naturalist. 50 The Canadian Field-Naturalist [Vol. 68 of the United States (1953); specific refer- ences are given for forms not included in this work, EUBRANCHIPODA Lepidurus arcticus (Pallas) S (1) After finding this spectacular Notostracan early during the trip we were on the look- out for it but its occurrence is apparently sporadic. It has previously been reported from more Northern locations (Johansen 1922). CLADOCERA The Cladocera were the best represented group in the collections. A total of 20 species was found and some of the animals occurred in great numbers, es
. The Canadian field-naturalist. 50 The Canadian Field-Naturalist [Vol. 68 of the United States (1953); specific refer- ences are given for forms not included in this work, EUBRANCHIPODA Lepidurus arcticus (Pallas) S (1) After finding this spectacular Notostracan early during the trip we were on the look- out for it but its occurrence is apparently sporadic. It has previously been reported from more Northern locations (Johansen 1922). CLADOCERA The Cladocera were the best represented group in the collections. A total of 20 species was found and some of the animals occurred in great numbers, especially Bosmina longispi- na and B. longirostris. Only in some collec- tions from small ponds and from one larger lake were Rotatoria more abundant than the Cladocera; Kellicottia (Notholca) Ion- gispina (Kellicot) being a representative spe- cies and also the most numerous. Holopedium gibherum Zaddach S (2) This organism, as was previously men- tioned, was only found in waters with a pH less than 7. Daphnia pulex middendorffiana Fischer S (3); G (6) This definitely Northern subspecies (Riser 1951) often with a brownish coloration on the dorsal part of the shell was fairly abund- ant, occurring more often in ponds than in lakes, yet it was never present in very large numbers. Daphnia pulex pulex (de Geer) G (1) Simocephalus vetulus (0. F. Mueller) G (3). Scapholeberis mucronata (0. F. Mueller S (2); G (1) Scapholeberis mucronata, var. fronte cornuta P. E. Mueller S (2). Both forms were numerous in the littoral regions of ponds. The horned variety had been mentioned by Herrick (1883) who conjectures that the sharp spine on the head (Figure 2) serves to clear away debris or detritus. No previous record from the North American continent is known to me. The Eurasian representatives of the variety "fronte cornuta" have a more pronounced horn — often almost as large as the head of the animal. Bosmina longirostris (0. F. Mueller) R (1); S (4); G (2). Bosmina longispina (L
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