2 12 THE AMERICAN MIDLAND NATURALIST 



study of color as one or the other group of naturahsts found 

 essential for constructive work. 



The writer's interest in the Naiades has been ecological as well 

 as systematic. In other papers, (3, 4, 5,), dealing with the Naiades 

 he has attempted to associate certain morphological features of 

 the shells with the physical conditions under which they lived. 

 A definite change of morphological features was found to parallel 

 changes in physical conditions. Morphological features of shell 

 are to the systematist, descriptive characters, as are also epidermal 

 and nacreous colors. It would therefore be worth while to look 

 for changes in the latter also to complete the idea of parallelism, 

 and if at the same time, some progress could be made toward 

 systematizing the color nomenclature as existing now in the 

 Naiades so much the better — especially if such could be done with 

 regard to any existing accepted scientific terminology, such as 

 that of Ridgeway. With this preliminary hint of the two-fold 

 scope of the observations to be given and the ultimate basis from 

 which it proceeded, we pass to a digest of the literature only with 

 which we are concerned, (the species dealt with in this paper), 

 as it is felt that the citation of even more fragmentary observations 

 about the other species of Naiades can add but little. At the same 

 time, it may be pointed out that in itself the literature cited largely 

 illustrates points which are the basis of conclusions later to be 

 taken. 



Wilson and Clark, (18-19), state that Unto gihhosus {Elliptio 

 dilaiatus), and Lampsilis, (Eurynia) rectus have a greater percent- 

 age of white nacre going down stream, (Maumee Drainage). Soft 

 water and amount of humic acid in the upper waters may favor a 

 purplish deposit, while colorless forms which occur shortly after 

 limestone beds are reached, may be found where there is an excess 

 of abundance of lime. . . . The rosy hue of Quadrula coccinea, 

 (Pleurobema coccineum) seems to be of a different nature going 

 down stream . . . the majority of this species from the Maumee 

 are white, few with a rosy nacre. Quadruh rubiginosa, (Fusconaja 

 flava) for the most part is white, but some are yellowish rosy. 

 In this drainage 2-3 of Unto gihhosus are white. Lampsilis rectus 

 had a purple nacre in some streams, white in others. In the Kan- 

 kakee Drainage, (19), upstream, Quadrula coccinea was found 

 to be of a delicate pink color, lower down becoming white, while 

 all shells of Elliptio in the upper part of the Kankakee Basin are of 



