ROTATORIA OF THE UNITED STATES. 
101 
parative study of the Rotifera of one of the swamps on South Bass Island and of those 
in the parts of Lake Erie immediately adjoining'. This swamp lies near the United 
States fish-hatchery, on a narrow point of land, so that the distance to the lake is not 
great on either side. On the east the lake is about 50 feet away, and the lake and 
the swamp are connected by a small channel. Under usual conditions the water tiows 
from the swamp through this channel into the lake. The swamp is shallow and its 
muddy bottom is covered by a dense growth of Geratophyllum , while its surface is 
completely mantled by Lemna , Spirodela , and Wolffia. In this swamp occurs a char- 
acteristic fauna, Rotifer tardus , Brachionus militarise Brachionvs bakeri , Apsilus, 
Monostyla quadridentata , Diplax trigona , Diglena bir aphis , Metopidia elirenbergii , Distyla 
gissensis , Notops clavulatus , Trochosplicera solstitialis , etc. Almost the only one of these 
that is common in the adjacent lake is the ubiquitous Monostyla quadridentata. Tow 
ings in the lake just outside the mouth of the swamp reveal Anurcea cochlearis , Synchceta 
stylata , Floscularia mutabilis , F. pelagica , Asplanclma priodonta, Notholca longispina , 
and other characteristic limnetic Rotifera, while the bottom of the lake has likewise 
a fauna differing markedly in character from that of the swamp. At certain times, 
under a northeast wind, the water of Lake Erie is driven toward the west end of the 
lake, where it rises much above the usual level. At these periods the direction of the 
current in the channel above mentioned is reversed, and water flows from the lake into 
the swamp, which therefore likewise rises a foot or more. At such times all the char- 
acteristic limnetic Rotifera of the lake above mentioned are found in the swamp. 
There is thus at intervals a thorough intermixing of the two faunas. Yet in a short 
time after the lake has returned to its usual level it is found that the swamp has again 
only its characteristic swamp fauna, while the limnetic forms from the lake have 
entirely disappeared. 
Certain rotifers thus require very special conditions of existence, and such condi- 
tions may exist only in a limited area, so that the rotifer will be confined to this area. 
Yet if the conditions do recur in any even distant part of the globe, the same rotifer 
is likely to be found there also. The history of Trochosplicera, for example (see p. 77), 
seems to bear out this conclusion. 
Dartmouth College, Hanover, N. H., May 29, 1899. 
