362 THE CANADIAN NATURALIST, [Vol. vi. 



Search, under the direction of Gen. C. B. Comstock, Superinten- 

 dent of the Lake Survey. Dredging was carried on from the 

 shallow waters, especially along the north shore, down to 169 

 fathoms, the deepest point known in the lake. In all the deeper 

 parts of the lake, the bottom, as shown both by the dredging and 

 by the soundings executed by the Survey, is covered with an 

 uniform deposit of clay, or clayey mud, usually very soft and 

 bluish or drab in color. Water brought from the bottom at many 

 points was perfectly fresh ; that from 169 fathoms gave no preci- 

 pitate with nitrate of silver. The temperature, everywhere below 

 30 or 40 fathoms, varied very little from 39^, while at surface 

 (at the time of the observations, during August) it varied from 

 50° to 55°. The fauna of the bottom corresponds with these 

 physical conditions. In the shallow waters, the species vary with 

 the varying character of the bottom, while below 30 to 40 fathoms, 

 where the deep-water fauna properly begins, the species seem to 

 be everywhere very uniformly distributed. The deep-water fauna, 

 as might be expected from the unfavorable character of the bot- 

 tom, is meager, and seems to be characterized rather by the 

 absence of many of the shore species than by forms peculiar to 

 itself. Some of the more interesting species occurring in deep 

 water were : 3Ii/sis relicta Loven, at various depths from 4 to 

 159 fathoms; Pontoporeia affinis Lindst., at nearly every haul 

 from the shallowest to the deepest; a small undescribed species of 

 Fisidium, down to 159 fathoms; several forms of dipterous 

 larvae, allied to Chironomus^ down to the same depth; several 

 species of Lumbriooid worms, of the genera Tiihi/ex, Scenurisy 

 and an allied genus ; and a species of Hydra, which was found 

 from the shore down to 159 fathoms. Of these, the My sis, Pon- 

 toporeia, and Pisidium are identical with species found by Dr. 

 Stimpson in his dredging in Lake Michigan, a short account of 

 which was published in the American Naturalist for September, 

 1870. The species of My sis and Pontoporeia I am unable to 

 distinguish from specimens from the Lake Wetter in Sweden. In 

 the Swedish lakes, these species were associated with Idotcea ento- 

 mon and Gainmaracanthus loricatus, marine species, and were 

 supposed by Lovdn to have been derived from ancient marine 

 species left in the lake basins by the recession of the ocean. The 

 occurrence of these forms in Lake Superior, so far removed from 

 the ocean, is certainly a very interesting fact in the geographical 

 distribution of species, but one which I will not attempt to discuss 



