MOLLUSC A. 139 



places where there is an alluvial deposit along the edges of the pond, 

 and the pond itself is choked with Potaviogeton nutans and bladder- 

 worts, so that a favorable habitat for acjuatic life has been formed. 

 These conditions have, of course, developed after the work on the quarry 

 was stopped, which was not many years ago, so that whatever shells 

 are now present have been planted in the last few years. The quaiTy 

 is not connected with any other ponds or swamps, and none of these 

 drain into it, so that the shells must have been introduced by accidental 

 means. 



The only shells found were Musculium securis, Pisidium ahditum, and 

 Planorbis parvus, but these were present in considerable numbers. 



Habitats of the Pigeon River. — 21. River portion. The Pigeon River 

 is a small, sluggish stream that winds around thru the clay country be- 

 tween Pigeon and Caseville, and down thru the sand dunes to empt\" 

 into Saginaw- Bay near the latter town. Thruout the last mile of its 

 course, the stream assumes the proportions of a small river as here the 

 slope is very gradual, the river being hardly above the level of the Bay. 

 This river portion is from three to six feet deep and in most places has 

 almost no current; in conseciuence, there is a luxurious growth of algae, 

 mosth' Vaucheria, along the bottom and sides, and a few of the higher 

 water-plants, especially Potamogeton nutans, in the more sluggish places. 

 The bottom, in these places, is muddy and soft, but contains some 

 gravel and boulders in the more rapid portions. (PI. X b.) 



Among the algae along the shores, a few specimen-s of Planorhis 

 hicarinatus. and numerous individuals of Sphaerivni striatinum, S. 

 solidulum, Planorhis parvus, P. trivolvis, Phy&a heterostropho , P. integra, 

 Amnicola limosa, Pisidium ahditum, and Succinea retusa, and many 

 small, juvenile specimens of Goniohasis livescens were found. From 

 places where the current was swifter, considerable numbers of Campe/oma 

 integra, Anodontoides feriissacianus suhcylindraceus, Lampsilis luteola, 

 and Quadrula unduJata, and single individuals of Anodonta grandis, A. 

 g. footiana, Lampsilis midtirodiata, L. iiis, and Quadrvla ruhiginosa 

 were discoA-ered partially buried in the clay along the shore and in the 

 gravel in deeper water. In addition, almost every rock was literally 

 covered with specimens of Goniohasis livescens. 



22. Bayou off the Pigeon River. Near its mouth the river made in 

 the past an "oxbow" bend about nine hundred yards long. Dm-ing the 

 da^^s when the river was used for floating logs, the small neck of land 

 separating the ends of the bend was cut thru in order to obtain more 

 current, leaving a typical oxbow pond, which has filled in at the upper 

 end so that it is only connected with the river at the lower end. This 

 pond is about six feet deep in the deepest place and is choked thruout 

 by a thick growth of vegetation, consisting of Potamogetons, etc.; along 



