146 Annals of the Carnegie Museum. 



usual scientific zeal most unselfishly contributed such of his own 

 observations as seemed to have a direct bearing upon the matter in 

 hand. Too much can not be said in appreciation of the kindness of 

 Dr. Ortmann, while almost equal indebtedness is felt tow^ard Dr. O. E. 

 Jennings of the Museum. 



From time to time I called upon other eminent and enthusiastic 

 students of the Naiades for the benefit of their experiences in certain 

 phases of the problem. Those who have cheerfully responded are 

 Dr. Bryant Walker, Dr. C. B. Davenport, Dr. A. F. Shira, Director 

 of the Biological Station at Fairport, Iowa, and Messrs. W. I. Utter- 

 back, Calvin Goodrich, and L. S. Frierson. Finally my thanks are 

 due to Miss D. M. Smith, a Y. M. C. A. Welfare Worker in France, 

 who aided considerably in the revision of the text. 



II. Introductory. 



The primary purpose of the investigation here recorded has been 

 to determine as precisely as possible in morphological terms what are 

 the distinctions which exist between the species of Naiades found in 

 the upper drainage of the Ohio River and their varieties in Lake Erie; 

 and secondarily by a comparative examination of these differences to 

 endeavor to reach definite conclusions as to the effects produced by 

 the two environments as causative of these differences. 



As with other classes of Mollusca, if we except such work as that 

 of C. C. Adams (i)* on the freshwater snail lo, the phases of local 

 variation in American species have received rather indifferent treat- 

 ment from zoologists. While they have been made the subject of 

 comment in a number of scattered papers by European investigators 

 dealing with American forms, they have principally received attention 

 in the more purely economic publications of the U. S. Bureau of 

 Fisheries, and there, as the examination of the literature shows, only 

 incidentally from an ecological rather than from a morphological 

 standpoint. 



L. V. Hueber (20) writing upon Unio fasciculus records physical 

 differences between individuals of this species found in rivers and 

 canals. He notes that the growth-lines are more distinct in the quieter 

 waters of canals; that, when viewed from in front, mussels from the 

 rivers appear wedge-shaped, those from the canals more oval. Julius 



* The numbers in parentheses refer to the Bibliography, Section XI of this 

 paper. 



