The American Midland Naturalist 



■aN 28 1921 



PUBLISHED BI-MONTHLY BY THE UNIVERSITY 

 OF NOTRE DAME, NOTRE DAME, INDIANA 



VOL. VI. NOVEMBER. 1920. N0-..,>Ja,» )5i«iS«* 



Variation in Epidermal Color of Certain Species of Najades Inhabiting 

 the Upper Ohio Drainage and their Corresponding Ones in L. Erie. 



BY N. M. GRIER, PH. D. 



I. — Introductory vStatement cf the Problem. 



This paper is a continuation of the study of the color problem 

 in certain species of Najades, first begun with an account of the 

 variation in nacreous color in the same species. (4). Besides the 

 major object as indicated in the title, now as previously an effort 

 will be made to show how the standard scientific Color Nomen- 

 clature of Ridgeway, (14), may be applied to the corresponding 

 descriptive characters of the species of Najades concerned. Again, 

 as it has already been shown that changes in the morphological 

 features of shells parallel changes in the accompanying physical 

 conditions under which they are found, (1,2), effort will be made to 

 show that in the epidermis of mussel shells, as well as in the nacre, 

 changes in color which may be similarly associated take place. 



The subject of the epidermal color of mussel shells does not 

 seem to have been made the subject of extended investigation. 

 V. Huber, (6), in studying some European and unrelated species 

 remarks that the epidermis of river forms is generally brown, but 

 at times a dirty green. Juveniles found in a subterranean canal 

 were greenish in color,. becoming black with age. v. Sell (15) 

 observed that the lake variety of Unio pictorum often had a green 

 coloring, (or rays), posteriorly, which was lacking in river forms 

 of the same species, v. Israel, (7), noted that the males of Unio 

 crassus were often reddish, while the females were gray. Marshall, 

 (9), states that "as a rule it may be said that the color of very 

 young specimens when not affected by foreign substances in the 

 water is a light or olive gray in the growing shell, gradually assuming 

 the colors by which it is known in the adult state." It is known 



