132 PAPERS ON ZOOLOGY OF MICHIGAN. 



common about the water plants: Sponges {Syongilla sp.), leeches 

 {PlacohdeUa rugosa and Haeniopsis niarmoratus) , snails {Physa hetero- 

 stropha), and insects {Lihellula pulchella, Somatachlora sp., Leucorhi- 

 nia intacta, Aeschna sp., Arciocorisa nitida, and Dytiscus sp.). 



Muck Bottom Shoals without Plants. The shoals, with deposits of 

 loose muck forming layers from a few inches to five or more feet thick 

 over hard, sandj' substrata were along much of the shore region of these 

 small lakes, but the layer is thickest in wind sheltered places such as 

 small bays. A good example of one of these is Station 55, which is a 

 bay running into the marsh on the northeast shore of Beaver Lake. 

 Here the muck is two or three feet thick with two feet or less of water 

 over it. The sand foundation is not down so far but that wading and 

 hence collecting can be easily done; and the muck is scarcely more 

 resistant than the water to a person going through it. The bay is 

 irregular in form and some seventy-five by a hundred feet in diameter. 

 It opens into the lake by a mouth about fifty feet wide. The sedges 

 of the marsh about it are nearly three feet high and form marginal 

 clumps (Plate XIX). The water is slightly bro^vn stained but free 

 from sediment and was found usually to have a temperature of 70° F. 

 This station has the largest and most constant fish population for its 

 size of any station studied in the Whitefish Point region, and it is 

 evident from general observations about the marsh lakes that the 

 conditions in this bay are those most attractive to the fish of these small 

 lakes. The following species were found here: red-bellied dace, 

 Cayuga minnow, black-head minnow, silvery minnow, Leiiciscus 

 7ieogaeus, Iowa darter, brook stickleback, common perch, homed dace, 

 white sucker, mud minnow, and common pike. 



The first five species listed associate closely with each other, forming- 

 dense, compact schools that tend to gather in peripheral depressions, 

 getting as near the marsh as possible but apparently not entering it. 

 They were probably finding food especia'ly abundant near it. Dis- 

 sections showed that diatoms, alga filaments, and insects were being 

 eaten. Sticklebacks were abundant and very generally distributed 

 in this bay; they were not in company with other fish or noticeably 

 with each other. They rest, apparently motionless, off the bottom, 

 and when the muck is disturbed they quickly gather about the cloud 

 so made, evidently looking for food. 



Only one mud minnow was caught and this in the minnow trap 

 placed on the bottom near the middle and deepest part of the bay. 

 This species may be abundant in this bay, but because of the habit of 

 hiding in the mud (Gill, 1904), few could be captured with nets. The 

 Iowa darters could be seen "creeping" over the surface of the muck 



