480 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
In August, 1885, 1 returned, again at Professor Baird’s request, with Prof. H. Gar- 
man, then my assistant, for some further studies bearing on the same subject. 
Fourth Lake, or Lake Mendota, Wisconsin, is the uppermost and largest of a chain 
of lovely glacial lakes lying about the State capital, finding an outlet through a 
small stream into Eock Eiver. It measures about 5| miles in greatest length, from 
east to west, and about 3^ in width, from “ University Landing” to the head of Cat- 
fish Bay. It is thus wider than Lake Geneva, but not so long, and is not nearly so 
deep. The deepest sounding made by me was but 79 feet, and the average of six 
soundings, well distributed over the trough of the lake, was 10 feet less. The bottom 
is more diversified than that of Lake Geneva, showing reefs of rock and of sand, and 
a large area of weedy shallows. Its waters consequently swarm with fish — especially 
with the common perch— and the amount and variety of invertebrate life is doubtless 
greater than in the more uniform Lake Geneva. The bottom in the deeper water is not 
different in character from that of the other lake, but is covered by the same soft cal- 
careous mud, with its peculiar little group of animal inhabitants. 
Catfish Bay, about a mile and a half across, and half as deep, is bordered by an ex- 
tensive marsh, which is drained by Catfish Creek, the principal feeder of the lake. 
There are about 80 acres of marsh at other points around the lake, but the shores are 
otherwise rolling, or even bluffy, especially in the narrower and deeper eastern 
division of the lake; and here are also several unfailing springs. Many other springs 
are said to open along the shores, below the water level. This lake differs from the others 
of the chain by the fact that it has much the largest drainage area and receives a larger 
affluent than any other; and this, as already said, drains a swamp. The waters 
of the lower lakes come mostly from Lake Mendota, in which they must have depos- 
ited much of their sediment, and where much of their organic matter must undergo 
decomposition before they flow off through its outlet. On the other hand, about 
three-fourths of the sewage of the city goes into Third Lake, or Lake Wenona, the 
next below. 
DREDGINGS. 
My general collections from the lake in 1884 were limited, by want of time, to 
three hauls of the dredge, made with the aid of a small steamer, one in shallow 
water (8 to 9 feet) on a sandy bottom, one on a rocky reef at a depth of 12 to 18 feet, 
and a third on a mud bottom at 12 to 12^- fathoms. 
The first haul, on a sandy bottom covered with Nitella^ yielded a great number of 
small white larvm of Ghironomm, with several small amphipod crustaceaus {Allor- 
chestes dentata), two or three small mollusks (Amnicola), a few worms {Stylaria 
lacii.stris), a single larval ephemerid [Gcenis), and two Entomostraea {Eurycercus lamel- 
latus and a species of Gypris.) The collection was a small one, the entire product a 
cubic half-inch. 
The haul on a rocky bottom gave only some small mollusks, not yet identified. 
The deep-water dredging gave precisely the same group of animal forms as those in 
the mud of Lake Geneva, namely, a good collection of Pisidium adamsi Pr., several 
large deep red Ghironomus larvae, and a species of the tube-making worm Limnodrilus. 
The principal collections of 1885 were made by nine hauls of the dredge, three of 
a fine-meshed seine, and seven of the surface net. 
Those from the deeper water did not differ in any way from those of the preceding 
