VARIATION IN NACREOUS COLOR OF NAIADES 219 



same collecting locality — such as the various stations at Presque 

 Isle, are apt to show a peculiarly distinctive nacreous color. 



Observation on Sex Correlative Coloration as Associated with 

 Nacreous Color * {27 Shells). 



Blues and Allied colors are twice as numerous in males than in 

 females. Females appear to have the more vivid pinks, while those 

 males even approximating the latter colors have reddish hues. 



2. — Amblema Plicata 

 In this species, particular attention was paid to the prevailing 

 hue of the iridescence at the posterior end, as the rest of the shell 

 is whitish. The rusty spots common in this species were ignored. 



SIMPSON RIDGEWAY 



Iridescence — Bluish Pearl Blue, 



Grayish Lavender, Pale Verbena Violet 

 Pale Vinaceous, Pale Salmon, 

 White. 

 Distribution of Colors as a Whole in Upper Ohio Drainage and 

 Lake Erie. (185 shells). 



Pearl Blue an4 allied colors.-.. 44% 



Grayish Lavender and allied colors.... 22% 



Pale Vinaceous and allied colors ....30% 



White 4% 



Distribution of Colors as a Whole in Upper Ohio Drainage 

 (107 shells). 



Pearl Blue and allied colors _ 45% 



Grayish Lavender and allied colors. 19% 



Pale Vinaceous and allied colors 36% 



Distribution of Colors as a Whole in Upper Ohio Tributaries, etc. 



Alle'nv Alle'ny Beaver Beaver Ohio 



Tribs. River Tribs. River River 



Pearl Blue and allied colors 50% 55% 20% 50% 33% 



Gray. Lavender and allied colors....i8% 22% 23% 



Pale Vinaceous and allied colors. .33%.. 22% 55% 50% 66% 



Distribution of Colors as a Whole in L. Erie. (78 shells). 



Pearl Blue and allied colors 50% 



Pale Verbena Violet and allied colors 33% 



Gray, Lavender and allied colors 11% 



Pale Salmon ! 6% 



* The small number of shells on which this and similar observations for 

 other species is due to the fact that most of the shells were collected before 

 Ortmann's discovery that the sex of these animals is readily determined 

 from cell structure. 



