Marsh—Limnetic Crustacea of (h^cen Lake. 183 
port, (Marsh, ’95, p. 4,) that Lake St. Clair has an immediate 
and constant connection with the deeper lakes, and there is, 
doubtless, continual migration into it of the forms characteris¬ 
tic of deep water. 
DESCRIPTION OF THE DREDGE. — PLATES XIII, XIY. 
The dredge which I have used was constructed after several 
experiments, and has, I think, answered admirably the require¬ 
ments of my work. Inasmuch as I expected to use it entirely 
for vertical work, it did not seem necessary that it should be 
closed when descending, but that there should be some device 
for closing it at any desired point on its upward course. The 
upper frame of the dredge is a brass ring from which by three 
cords is suspended the bucket. The upper frame is thirty-one 
centimeters in diameter. 
The bucket is like that described by Professor Birge. (Birge, 
’95, p. 428). Inasmuch as the wire gauze used in the bucket 
has meshes 1-100 of an inch in diameter, it does not retain the 
smallest organisms, but serves perfectly well as an apparatus 
for catching Crustacea. 
The dredge bag is of India linen, carefully selected so as to 
get cloth that is fairly uniform in texture, and is suspended 
between the upper frame and the bucket. The dredge bag is 
strengthened on its upper edge by heavy cloth, into which are 
let the eyelets, by which it is laced to the brass rings of the 
frame. 
The cords between the frame and the bucket are continued be¬ 
low the bucket and fastened to a sounding lead weighing about 
six pounds. To the upper frame are attached three cords which 
unite in a brass ring, by which the dredge is suspended by the 
releasing apparatus. About half way of the length of the dredge 
there are attached to the suspending cords brass rings, through 
which a cord runs twice in such a way that when it is drawn 
tight it acts like a puckering string and closes the dredge. 
This cord is attached to the dredge rope, which, after being 
fastened to the releasing apparatus, hangs loosely over the edge 
of the dredge. 
The releasing apparatus consists of a brass frame (see PL 
