404 ON THE DEEP-WATER FAUNA OF LAKE MICHIGAN. 
ingly on the 24th of June last we started out from Racine 
for the purpose in a tug belonging to that place. The party 
consisted of Dr. Lapham, Dr. Hoy, Mr. Blatchford and Dr. 
Andrews of Chicago, and myself. We dredged at various 
points from twelve to twenty-six miles from land, the great- 
est depth found being sixty-four fathoms, with a bottom of 
blackish impalpable mud. Between the distances of twelve 
and twenty-two miles from shore the depth was tolerably 
uniform, averaging forty-five fathoms, the bottom being 
generally a reddish or brownish, sandy mud. On this 
plateau we obtained alive the crustacea found by Dr. Hoy in 
the stomachs of the whitefish, consisting of a Mysis and two 
species of Gammarus. A small white Planaria, and a new 
species of Pisidium also occurred. All of these animals 
were found in abundance, showing this portion of the lake 
bottom to be rather densely inhabited. 
Mysis is a marine genus, many species of which occur in 
the colder parts of the North Atlantie and in the Arctic 
seas. One species, M. relicta, was found by Lovén in com- 
pany with Zdothea entomon and other marine crustacea in 
the deep fresh-water lakes, Wenner and Wetter of Sweden, 
indicating that these basins were formerly filled with salt- 
water, and have been isolated from the sea by the elevatory 
movement of the Skandinavian peninsula which is still go- 
ing on. That the same thing has occurred to our own lakes 
is shown by the occurrence in their depths of the genus 
Mysis, notwithstanding the non-occurrence of marine shells 
in the quaternary deposits on their shores. Kingston on 
Lake Ontario, is, I believe, the highest point in the valley 
at which such shells have been found. Very probably, at 
the time when the sea had access to these basins, the com- 
munication was somewhat narrow and deep, and the influx 
of fresh-water from the surrounding country was sufficient 
to occupy entirely the upper stratum, while the heavier sea- 
water remained at the bottom. After the basins had become 
separated from the ocean by the rise of the land, the bottom 
