Marsh — Limnetic Crustacea of Green 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, XIV. 



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 PI. 



