No. 503] ECOLOGY OF 1! EC EXT CBINOIDS 



723 



sometroida, the other with round pinnules and large eggs, 

 the Antedonoida. The forms with small eggs, being no 

 smaller than those with large eggs, may reasonably be 

 supposed to require a longer period for development. 

 This would imply a greater duration of the free swim- 

 ming larval period, which would result in greater powers 

 of dispersal, hence a greater geographic range. More- 

 over, a slowly developing larva might he supposed to 

 possess a greater power of adaptation to environment, 

 and therefore a certain ability to colonize new places un- 

 der changed conditions, for instance, to spread down- 

 ward to great depths. 



The genus Thalassometra, genus of the Thalas- 

 sometroida (with small eggs) has the widest distribution 

 of any comatulid genus known, geographically and 

 bathy metrically. It is found throughout the tropics, 

 northward to the Aleutian Islands, the West Indies and 

 Portugal, and southward to South Africa, the Crozet 

 Islands and Australia; in depth it ranges from about 

 50 to l,f)00 fathoms. Charitometra and Tropiometra, 

 two other genera of the same group, are both inter- 

 tropical, and the former readies very considerable depths. 

 The genera belonging to the Antedonoida (with large 

 eggs) are mainly comparatively local and do not occupy 

 large bathvmetric altitudes. Though a number are 

 littoral and one inhabits the greatest depths from which 

 crinoids are now known, the bathvmetric range of each 

 is small, far smaller than that of the genera of Thalas- 

 sometroida. 



The beautiful and brilliant coloration of the crinoids 

 has often been remarked ; so striking is the common Euro- 

 pean species, Antedon bifida, that it has formed the sub- 

 ject of colored plates by Heusinger, Dujardin, Dalyell, 

 Dujardin and Hupe, and Gosse; but the larger tropical 

 species are much more varied and handsome (though 

 colored figures of them have been published only by 



