VARIATION IN EPIDERMAL COLOR OF NAJADES. 249 



the old bed of a stream defunct several years ago. But the small 

 streams which feed this lake and which cease to flow during droughts 

 both produce an abundant crop of Anodons. Now in the lake, these 

 grow to a large size, much inflated, smooth, somewhat rayed, 

 brightly colored. But in the pools of the headwaters, creeks ten 

 to fifteen feet deep, thirty feet wide, covered with trees, full of 

 decaying leaves and black mud, grow shells elongate, compressed, 

 rough, black and hardly to be differentiated from Unio comptodon 

 by its external appearance. Yet they are no doubt the same species, 

 or no doubt frequently mother and daughter. This is environment." 



F'ollowing the clues given in the foregoing, effort will be made in 

 this paper to throw light on the following problems connected with 

 the color of the epidermis in the species of Najades dealt with: 



I. In those species commonly assigned more than one epidermal 

 color, to determine as far as possible the relative prevalence of each 

 color in all the shells as a whole, and the difference between L. Erie 

 and Upper Ohio shells in this regard. 



2. (a.) To ascertain whether any change in epidermal color takes 

 place going down stream, both in the rivers and in their tributaries 

 and to learn whether in any of the species a particular shade of the 

 described epidermal color is peculiar to the body of water concerned, 

 (b.) To study the prevalence and qualities of the rays of the 

 epidermis under conditions indicated for this and the preceding problem. 



3. As a partial check on problems one and two as well as for their 

 own biological interest to show, (a) any relation existing between the 

 epidermal colors and the estimated age of the animals; (b) any associa- 

 tion of the epidermal colors with their sex. 



II. — List oe Species Used. 



LAKE ERIE UPPER OHIO DRAINAGE 



Fusconaja flava parvula, Crier Fiisconaja flava, Rafinesque. 



Amblema plicata, Say. Amblema costala, Rafinesque. 



Pleurobema ohliquuni pauperctilum, Pleurobe'ma obliquum coccineum, Con- 

 Simpson rad. 



Elliptio dilatatus sterkii, Crier Elliptio dilalalus, Raj. 



Symphynota costata eriganensis, Crier Symphynota costaia, Raf. 



Anodonta grandis foofiana, Lea. Anodonta grandis, Say. 



Paraptera fragilis, Raf. Parapiera fragilis, Raf. 



Proptera alata, Say. Proplcra alata, Say. 



Anodontoides ferrussacianus subcylin- Anodontoides fertissacianus, Lea. 

 dricus, Lea. 



Eurynia recta, Lamarck. Eurynia recta latissima, Rafinesque. 



