126 PAPERS ON ZOOLOGY OF MICHIGAN. 



upper end of the series plants are especially numerous and form a small 

 marsh (Station 172, Plate XVIB). A short distance above this a 

 beaver dam is across the creek near where it emerges from the Avoods 

 (Plate XVB). The dam is a new one and has .caused the creek to 

 flood a large wooded area recently. Below the dam is a pool (Station 

 171, Plate XVB). 



Much invertebrate life was in evidence about these pools and m^arshes. 

 The following aquatic forms were taken in the net Avith fish collections : 

 dragon-fl}^ larvae (Aeschna, Somatochlora , Goynyhus), water striders 

 {Gerris remiges), and leeches (Macrobdella decora, Haemopsis mar- 

 moratus, and Placobdella rugosa). Attached to inany submerged ob- 

 jects were sponges (SpongiUa frag His). A protozoan {Stentor igneus) 

 swarmed near the water surface, giving a considerable area of it a bright 

 green color. 



The noticeable vertebrates were frogs, tadpoles and a number of 

 birds. In general four types of fish habitats are present: (1) the deeper, 

 open water areas; with water about three feet deep and a hard sand 

 bottom, over which there is little debris or humus; water plants are 

 absent, except a few small patches of stoneworts or bladderworts, (2) 

 the marsh region, with a thick growth of partly submerged sedges, 

 rushes, flags, sweet gale, and a number of others and also much green 

 algae on the surface and much stonewort beneath it, (3) marginal 

 areas of very shallow water, two or three inches deep, and unusually 

 warm, and well exposed to sunlight owing to a scarcity of seed plants, 

 and (4) the pool beneath the beaver dam (Station 171, Plate XVB), 

 which is about twenty by thirty feet with a depth of about three feet 

 down to the sand bottom, over which there is a foot or more of dead 

 leaves, sticks, and other litter, and growths of stonewort; the water 

 was cold (65° F.) and stagnant, since the pool is supplied by percola- 

 tions through the beaver dam. 



In the open deep areas (No. 1, above), the following fish were taken: 

 black-head minnow, Cayuga minnow, horned dace, Leuciscus neogaeus, 

 black-nosed dace, and brook stickleback. 



None of these were abundant or generally distributed in this tj^pe of 

 region. The Cayuga minnows were chiefly in a few large schools in 

 the deepest water; and those observed were large examples of their 

 species, while all the other fish taken were much undersized. 



In the marsh area (No. 2, above), chiefly in the more open places, the 

 following fish were caught: red-bellied dace, silvery minnow, black- 

 head minnow, horned dace, Leuciscus neogaeus, Cayuga minnow, black- 

 nosed dace, mud minnow, and brook stickleback. 



Most of these fish were small, under an inch in length, and each 

 species, except Cayuga minnows, L. neogaeus, and mud minnows, was 



