257 



dermis of the mussel clean. In other cases it adheres more closely and 

 is difficult to scrape off clean. On this marly growth, colonies of 

 Opfn-ydium, much the size, color, and general appearance of grapes 

 with the skin removed, are often found growing, and in the cavities and 

 interstices of the marl, a handsome little water-beetle, Stenehnis sulcatus 

 Blatchley, and its peculiar elongate black larvae, lives in considerable 

 numbers but apparently has nothing to do with the mussels. Various 

 species of hydrachnids, one of them strikingly handsome with its green 

 body sprinkled with bright red dots, also live in the cavity of the marl, 

 and offer some suggestion as to how the parasitic mite Atax went a 

 step farther and took up its habitation within the mussel itself. 



Food and Feeding. — An examination of the stomach and intestinal 

 contents of the various species of mussels of the lake .showed no notice- 

 able difference between the food of the different species. Enough of 

 the bottom mud is generally present to give the food mass the color of 

 the bottom on which the mussels are found. Thus the stomach-contents 

 of the mussels found in the black bottom of Lost Lake were usually 

 blackish, while that of those found in the lighter bottom at Long Point 

 were grayish. Intermixed, however, with the whole mass was always 

 enough algas to give it a somewhat greenish tinge, this green being 

 usually intermixed more or less in the form of flakes. A striking con- 

 trast between the stomach contents of mussels inhabiting lakes and 

 those found in rivers is the much greater preponderance of organic 

 matter in the food of the lake mussels. The stomach contents of river- 

 mussels is generally chiefly mud, with a few diatoms, desmids, Sce- 

 nedsmus and Pediastrum intermixed, as said above. Those of the lake 

 mussels are almost always full enough of algae to be more or less flecked 

 with green and sometimes the whole mass is decidedly greenish. On 

 being placed in a vial of preserving fluid (3 per cent formalin was gen- 

 erally used) and shaken, the material from the river mussels always 

 retains the uniform appearance of mud; that from the lake mussels 

 separates, the mud settling to the bottom and the organic material 

 settling as a light flocculent mass above the more solid portion. This 

 top layer is composed of the various plankton elements of the lake, and 

 was found to vary considerably in different lakes. In the Lake Maxin- 

 kuckee mussels it was found to consist chiefly of such species as Mi- 

 ll— 11994: 



