746 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The greenish tinge in Phrynocrinus and Calamocrinm seems to result from 

 the dusky age factor as seen through the normal brilliant yellow, while the " dusk}' 

 purple " is possibly the age factor as modified by semiopaque white, and therefore 

 comparable to the dusky purple spots seen in the eggs of such birds as the Tyran- 

 nida? and Laridse. 



4. Illumination of the habitat results in 



(a) An intensification of the natural colors and the very early appearance of 

 the dusky age factor. 



The original color may be uniformly intensified, or the intensification may be 

 more or less localized, resulting in the formation of blotches, spots, or bands. 



Individuals from dark muddy bottoms or from deep holes or other shaded 

 situations are much lighter and less diversified in color than individuals of the 

 same species from bottoms of broken shells, coral reefs, or other brilliantly illumi- 

 nated locations. On coral reefs it has been noticed also that even very small 

 specimens are often very dark in color. 



(b) The appearance of a blue factor, resulting in the formation of bright 

 greens, purples, and violet, which may deepen to black. 



All the crinoids living below the limit of light penetration exhibit the basic 

 colors, white, yellow, orange, or red only, which, though they may become more 

 intense toward the calyx and arm bases, are never otherwise diversified. Each 

 of these colors, however, may be modified by the dusky age factor, resulting in 

 " dusky purple," greenish or brownish yellow, brown, orange brown, crimson, or 

 red brown. The blue factor is absent from these species, but in the group as a 

 whole it gradually increases from the limit of light penetration to the surface, 

 causing the appearance of greens, purples, and violets of increasing intensity. 



The development of color in the crinoids may be represented by the follow- 

 ing scheme : 



With the addition of the With the addition of the dusky 



blue factor becoming factor becoming 



/bluish gray gray. 



~1 gray to "dusky purple." 



[bright greenish yellow ....grayish green. 



[bright green ..brownish green. 



Yellow 



greenish. 



brownish yellow. 

 I. yellowish brown. 

 I brown. 



forange purple purplish brown. 



f I orange violet violet brown. 



..orange brown. 



purple purple brown. 



[violet brown. 

 K.-I violet. | blnck . 



j red brown. 



5. Temperature plays no part in the development of color in the crinoids. 



