214 THE AMERICAN MIDLAND NATURALIST 



Ohio Drainage and Lake Erie. The material used was collected 

 by Dr. A. E. Ortmann over a number of years, (1903-07), in Western 

 Pennsylvania and Lake Erie, or secured by him in smaller amount 

 as exchanges. Dr. Ortmann, besides suggesting the value of an 

 introductory study to the color problem in Naiades, has done 

 everything in his power to assist the investigation, for which data 

 was obtained at the Carnegie Museum, Pittsburgh. I am also 

 indebted to Dr. W. J. Holland, Director of the Carnegie Museum 

 for the freest use of its facilities in connection. 



III. — Physical Conditions and Type of Mussel Fauna. 



The type of Mussel Fauna has already been admirably treated 

 in papers by Walker, (17) and Ortmann, (12). These and the 

 physical conditions concerned have already been summarized by 

 the writer elsewhere, (5); the latter are ably given for L. Erie by 

 Jennings (8), and for the Upper Ohio Drainage in the Water 

 Supply papers of the U. S. Geological Survey (6). For sake of 

 convenience, however, the outstanding points concerning the 

 physical conditions are given in the following, contrasting columns. 



LAKE ERIE UPPER OHIO DRAINAGE 



Water colder than in Upper Ohio, Water warmer, hut greater extremes 

 but with more even regulation of tem- of temperature to face. Streams more 

 perature. Currents much less rapid rapid than current of L. Erie; greater 

 than in streams, less agitated, except agitation, frequent falls and rapids, 

 by very moderate currents, carrying short stretches of quiet pools. River 

 but little sediment. Bottom pebbles carry a load of debris moving quickly 

 or sand or mixture of these, depending over the bottom which consists of 

 on region of lake, with coarser sedi- mud, glacial fill, cobbles. Food 

 ment derived from wear of land. cotiditions, (due to extreme of tern- 

 Temperature conditions favor a more perature), are less stable, even if 

 uniform production of food, while at times food is more abundant, 

 the water contains more lime. 



It may be added that L. Erie shells as a whole have been observed 

 to possess brighter (clearer) colors than their fellows of the Upper 

 Ohio Drainage, are exceptionally polished, and otherwise charac- 

 terized in distinction by their well developed lines of growth. Dr. 

 Walker in a letter to the writer, (1914) suggested that certain 

 depauperate qualities of the L. Erie shells may be due to the chemi- 

 cal quality of the water, pointing out that the influence of brackish 

 water upon fiuviatile species is well known. The relation of this 

 fact to the color problem will be dealt with later. 



