VARIATION IN NACREOUS COLOR OF NAIADES 235 



Pale Grayish Blue Violet, etc 13% 



Pale Purplish Vinaceous, etc 17% 



Distribution in Lake Erie — Localities, and Chautauqua Lake. 



La Plaisance Cedar Presque Chaulaugua 



Bay Point Isle Lake 



Pearl Blue, etc. .' 25 % 24% 25 % 40% 



Light Pinkish Lilac, etc 25 % 32 % 42% 35 % 



Pale Pinkish Vinaceous, etc -...37% 33% 13% 25% 



Pale Grayish Blue Violet, etc 12% 1 1 %...... 20% 



Deductions from Tables of Percentages and PI. III. 



Pearl Blue and White are most abundant in L. Erie and there is 

 less Pinkish Lilac or Purplish colors, as well as more Pale Grayish 

 Blue Violet are most peculiar to the Upper Ohio drainage. 

 In the Upper Ohio Drainage: 



The rivers have more Pearl Blue and White than the tribs. but 

 less Light Pinkish Lilac and less Pale Grayish Blue Violet. General 

 shades of Pinks and Pearl Blues are about evenly distributed 

 throughout this drainage. About the same percentage of blues 

 exists in the Allegheny and Beaver Drainages, while White is most 

 abundant in the Ohio, — ^apparently an outstanding exception to the 

 general rule. Fading is seen going down stream in the Allegheny, 

 Ohio, Shenango, and Little Beaver Rivers. Characteristic stream 

 colors are best indicated in PI. III. 

 In Lake Erie: 



Here white and pearl blues are practically equivalent. Most of 

 the Light Pinkish Lilac colors are at Presque Isle Bay; Pale Purplish 

 Vinaceous in La Plaisance Bay; while Cedar Point has more 

 purplish colors than Presque Isle, it has less than La Plaisance Bay. 



Pearl Blue predominates in Chatauqua Lake. 



Observation on Sex. Correlative Coloration, etc. {84 shells). 

 Males may either be white, pinkish lilac or pearl blue. 

 Females are purplish vinaceous. 



VI. — ^Conclusions. 



1. In certain species, (as may be inferred from the table dealing 

 with the distribution of colors as a whole), there exists a wider 

 range of variation of nacreous color than is indicated by standard 

 specific descriptions. 



2. In practically all the species dealt with, a change in nacreous 

 color is observed going down stream from the headwaters to the 



