Cladocera 5 E 



Daphnia longispina var. hyalina forma arctica nova forma. 



Six plankton catches (vertical hauls) obtained from big lake (see fig. 3) at 

 Bernard harbour, Northwest Territories, between September 30, 1915, and June 

 12, 1916, contain a diminiitive form of the variety hyalina which is characterized 

 chiefly by its small size. The crest of this form is small and regularly rounded 

 so that the eye is situated near the anterior margin and only a little below the 

 middle of the head. The ventral margin of the head is slightly concave and the 

 dorsal margin of the shell shows a slight concavity just above the heart. (See 

 figures 1 and 2.) 



FIG. 1. Daphnia longispina var. hyalina forma arctica nov. forma. 

 Big Lake, Bernard harbour, Northwest Territories, 

 September 30, 1915. Length, exclusive of spine, 0.97 

 mm. 



The egg-bearing females obtained in September range in length from 0-9 

 mm. to 1-0 mm., exclusive of the spine, while the February specimens vary 

 from 0-7 mm. to a little more than 0-8 mm. The spine is from a half to two- 

 thirds as long as the body. No ephippial females were noted in any of the 

 catches from this lake, but six of the samples contained parthenogenetic 

 females; the majority of the latter carried only two eggs while a few bore as 

 many as three, and others only one. Wesenberg-Lund also found that the 

 parthenogenetic females of Daphnia longispina belonging to the microcephala- 

 galeata group, in plankton material from Thingvallavatn lake, Iceland, carried 

 but two or three eggs. 



FIG. 2. Daphnia longispina var, hyalina forma arctica. Big 

 Lake, Bernard harbour, Northwest Territories, 

 February 12, 1916. Length, exclusive of spine, 

 0.77mm. 



Egg-bearing females were noted in catches obtained from the lake at 

 Bernard harbour on the following dates: 



1. September 30, 1915. Ice eight inches, depth of water 19 feet. Many. 

 . 2. November 28, 1915. Ice about two feet. Temperature of water at 

 surface 32 F., below surface 32-5. Few. 



3. February 12, 1916. Ice 5-5 feet, depth of water 20 feet. Temperature 

 of water at surface 32 F., air 20. Few. 



