278 Dr. H. A. Nicholson on Brcdgings in Lake Ontario. 



Another series of dredgings was taken along a line extend- 

 ing in a south-west direction, from Toronto Point to a point 

 about five miles out in the lake, the depths varying from 8 

 to 15 fathoms. In this case the bottom was found uni- 

 formly to consist of an exceedingly fine, bluish-grey, clayey 

 mud, with numerous patches of a small bushy Alga (a species 

 of Cladophora). The mud contained very numerous minute 

 Annelides of the genus Swnuris, along with dead shells of 

 CyclaSj Pisidiwn^ and Planorhis ; and the bunches of Clado- 

 jphora yielded a large number of little Ostracode Crustaceans, 

 and a few beautiful little Amphipods which are as yet unde- 

 termined. 



Another series of dredgings was carried on still further to 

 the south-west of the ground examined, in the series just men- 

 tioned, at a distance of about eight miles from the shore. The 

 depth here varies from 30 to 45 or 50 fathoms ; and the bottom 

 was found to consist uniformly of a fine greyish mud, some- 

 times highly argillaceous, sometimes more or less arenaceous, 

 with many small pebbles disseminated through it, and con- 

 taining a few dead shells of Planorhis and Pisidium^ and 

 much broken-down vegetable debris. Every haul also brought 

 up numerous specimens of a beautiful flesh-coloured Amphi- 

 pod and a few minute Annelides ; but no other traces of life 

 were obtained. The Amphipods are referable to Pontoporeia^ 

 being apparently undistinguishable from P. affinisoi the Swe- 

 dish lakes ; and I shall speak of them at greater length imme- 

 diately. 



Another series of dredgings were taken in Humber Bay, 

 about four miles to the west of Toronto. Here the bottom, 

 except close to the shore, consisted of a tenacious bluish-grey 

 clay, sometimes with reddish patches in it. Vegetable life was 

 very scanty ; and animal life consisted entirely of many minute 

 Annelides. 



Lastly, an examination was made, partly with the dredge 

 and partly by means of a hand-net, of the shallow water in 

 the immediate neighbourhood of the " island " and of the ex- 

 tensive ponds which communicate with the lake. The bottom 

 here consisted, for the most part, of a black mud composed 

 almost entirely of decayed vegetable matter, and supporting a 

 dense growth of Charas, Vallisneriaj Anacharisj Pontederia, 

 Nymphaja^ and Nuj)har. Animal life was naturally extremely 

 abundant, comprising numerous examples of Limnoia, Physaj 

 Planorhis^ Paludina^ Ci/clas, Pisidmm^ and Anodon^ along 

 with two species of Gammarus and many small Ostracode 

 -Crustaceans, a few leeches {Clepsine), very many large scarlet 

 water-mites, numerous aquatic insects {Nepa, Gyrinus, Dy- 



