No. 503] 



ECOLOGY OF RECENT CRINOIDS 



725 



Brown: Very large specimens of all the species of 

 Thalassometrida?, Thaumatometra, and Thysanometra. 



Under the second heading come, Zenometra, Psathyro- 

 metra, Bathymetra, Isometra, the Pentametrocrinidae and 

 Hypalocrinus. 



No species is known which exhibits a perfect blending 

 of these two basic types or their derivatives, though 

 there are many mosaics in which both are found side by 

 side, either in different individuals, or, more usually, in 

 the form of a color pattern, made up partly from one 

 base and partly from the other (each being clearly de- 

 fined) in the same individual. 



Some mosaic species, such as Tropiometra afra and 

 certain of the Comasteridae are peculiar in that some 

 specimens belong exclusively to type I (yellow) and 

 others exclusively to type II (violet) but none are ever 

 mixed. 



The mosaics are, the Zygometrida\ the Comasteridae, the 

 Thopimetridae except Asterometra, Iridometra, Antedon, 

 Erythrometra, Perometra, Hypalometra, Promachocrinus, 

 and the Himerometrida*. 



The data seem to show that the smaller stalked forms 

 are invariably and unchangeably yellow, which color may 

 be, as in the case of the parrots among birds, equivalent 

 to a lack of color. Black is added to the basic color of 

 comatulids at all depths, and appears to denote age. 

 Blue is added apparently only within 200 fathoms of the 

 surface, and increases in intensity to the surface. The 

 mosaics are all littoral or shallow water types. 



Species growing among coral or on white bottoms in 

 shallow water are very dark in color, often nearly black 

 or sharply black and white, while the same species on 

 mud may be light yellow and pinkish; or a species may 

 be purple and yellow in comparatively deep water, and 

 violet and white in shallow water. We seem to be able 

 to trace a close connection between color and amount of 

 illumination, the blue factor in the coloration increasing 



