258 



crocysUt xruyinosa, Botryoccus braunii, Coslosphxrium kuetzingia- 

 num, various diatoms, such as species of Navicula, Rhoicosphenia, Gom- 

 phenema, Cyclotella, and Cocconema, various forms of desmids, espe- 

 cially Cosmdrium and Staurastrum, various forms of Scenedesmus, 

 considerable Peridiniuni tabulatum, and short filaments of Lyngbya. 

 Pediastrum, both boryaniim and duplex, are here, as almost everjrwhere, 

 rather common objects encountered in the intestines of mussels. Casts 

 of the rotifer Anursea cochlearis, and one of the small entomostracan, 

 Chydorus, were occasionally encountered. In one of the Lost Lake mus- 

 sels, Dinobryon, an exceedingly frequent element of the mussel-food in 

 Lake Amelia, Minn., but rare here, was found. 



No opportunities were had to study the stomach contents during 

 the winter, the mussel work having not been taken up to any extent 

 during the earlier part of the sui-vey. Mussels obtained quite late in 

 autumn contained much the same material as in summer. The open 

 and apparently active inhalent and exhalent apertures noted through- 

 out the winter in some individuals would indicate that the mussels — at 

 least some of them — do not hibernate, but carry on life processes more 

 or less actively the year round. The presence of pretty well-marked 

 growth rings would indicate, however, annual rest periods. As diatoms 

 appear to be much more abundant in the water during the winter, it is 

 probable that they enter more plentifully into the mussel's bill-of-fare 

 during the late autumn, winter, and early spring, than during the sum- 

 mer. In considering the mussels as feeders on plankton elements, it is 

 worth while to investigate whether these are not of benefit to the lake 

 as reducers of the excessive amounts of such undesii'able elements as 

 Lyngbya, Anubsena and Microcystis, and whether a considerable in- 

 crease in the mussel population by means of artificial propagation would 

 not clear up the lake to a considerable extent. 



The following studies of stomach contents and table of mussel food 

 are by no means exhaustive, but represent hurried examinations and a 

 record of the more easily recognized forms out of a mass of doubtful 

 material. They are intended to be simply suggestive. 



Closely connected with the question of food and nutrition is that of 

 the size of the mussels. A marked feature of the mussels of Lake 

 Maxinkuckee, as well as of the neighboring lakes, is the dwarfing of 

 many of the species, and this is rather difficult to explain when one 



