VARIATION IN NACREOUS COLOR OF NAIADES 24 1 



with age, most of them tending to revert back to the "pearl blue 

 or whitish" ground color. Similar treatment of L. Erie shells apart 

 from those of the Upper Ohio corroborate this finding. But to be 

 considered with such a generalization, is the fact that very fre- 

 quently large nos. of shells of different ages from the same locality 

 show an almost uniform nacre color. 



IX. Relative Variation in Nacreous Color in the Species 



Dealt "With. 

 The shells were so unevenly distributed with regard to localities, 

 that it was impossible to determine those pl'aces where the greatest 

 amount of nacreous color took place. Some idea may be obtained 

 from PI. III. In an effort to make a balanced determination of the 

 relative variability of nacreous color among them a rough and 

 arbitrary comparison was taken by dividing the number of "relative 

 colors" observed in each shell by the number of that species ex- 

 amined. Rough as the writer feels his methods to have been in 

 exploring this uncharted field, it seems that within the limits of 

 this investigation that the larger number of shells is apparently 

 associated with less variation in nacre color. At the same time, 

 these results are hardly fair for those species represented by a 

 small number of specimens. Results from this method show the 

 relative variability of the shells to be as indicated in the following 

 table. 



No. of Relative No. of , Factor 



Colors Taken Shells Colculaled 



Euryma recta 29 _ .54. 



2. Propter a alata 26.__ ---55 



J. Paraptera fragilis.. 23 53 



4. P. ohUqtium coccin 53 263 ^ 



5. Amhlema plicata..... 35 185 



6. Anodont ferrussacianus.... 8 45 17 



7. Anodonta grandis ...19 1 19 .16 



8. Fusconaja flava... 40 273 14 



g. Lampsilis ovata ...31....S 214. 14 



10. Elliptio dilatatus. 76 561.... 13 



11 . Symphynota costata 19 68 .13 



12. Lampsilis luteola. 26 289 09 



A similar study of variation in Epidermal Color in the animals is expected 



to appear in a later number of this publication. 



and Anodontoides, while the purples tend to disappear. Eurynia, L. luteola, 

 and L. ovata appear to retain their vivid colors to later age than the rest 

 of the species, but all of the latter tend to revert to "bluish-white." 



