VARIATION IN EPIDERMAL COLOR IN NAJADES. 277 



Buffy Olive 25% 25%..... .._. 50% 



Brownish Olive 25 % 25 % 25 % 



Buffy Citrine :--25% 



Mars Brown 25% 



Dark Olive Buff 25% 



Deductions from Tables of Percentages and PI. III. 



Yellow and Yellow Green colors are prominent in L. Erie; browns 

 in the Upper Ohio. • 



In the Upper Ohio Drainage 



A tendency to darken both in primary and secondary colors is 

 seen descending the Allegheny^ — from yellowish to brownish or 

 buflf colors. This is the general change found also in the course 

 of the Crooked and Neshannock Creeks; Ohio, Shenango and 

 Mahoning Rivers. In most cases the shells of the tributaries will 

 be found to have lighter colors than those of the main streams. Char- 

 acteristic primary stream*" colors are Olive Lake in the Allegheny, 

 Isabella Color in the Ohio, Olive Ochre in the Shenango, Olive 

 Yellow in the Mahoning, Buffy Citrine in the Little Beaver. 

 In L. Erie 



Yellows appear to be equally abundant at all the lake stations 

 given, Ibut these differ in their proportions of Buffy and Brownish 

 Colors. Chautauqua Lake seems characterized by an abundance 

 of the former. As was found with nacreous color, this and the last 

 named species show little variation in epidermal color. 

 Rays of Epidermis 



Simpson: "Broad bright green rays, wanting in older shells." 

 140 of 180 shells were rayed. Coarse rays were most abundant in 

 lake specimens, medium and fine rays in the rivers, with coarse 

 and medium textures about equally divided in the creeks. Colors, 

 yellow to dark green, with a tendency toward black in the Upper 

 Ohio Drainage. Coarse and fine rays are most abundant in male 

 shells; medium in female. 



Relation of Epidermal Color to Estimated Age of Animal. 



No juveniles were comprised in the material worked with. 

 Green is most abundant in shells beneath 12 years of age. Greenish 

 yellow appears to increase in older shells in both L. Erie and the 

 Upper Ohio Drainages. Shells may become brown or black as early 

 as 1 1 years, although such colors are not abundant in either of the 

 LampsiHne shells possibly due to their more highly polished epi- 



