8 Eci!lNOnERMA OF THE INDIAN ^lUSEUM, PART VII. 



littoral species which would tend to attract tliese small organisms. .Many criiioids 

 are concentrically banded, and this, too, may attract the smaller marine animals, 

 just as contrast spots on flowers do insects. In the north and in the south the 

 maximum intensity of marine life is at and just Itelow the surface, l)ut in tlie 

 tropics the lethal effect of the brilliant sunlight forces it dovvnward nearly to the 

 200-fathom mark. The crinoids, are of course, affected with the other organisms, 

 but many of them cannot descend to that depth. They therefore lurk in dark 

 holes under rocks, or, especially, in caves or under wharves, the darkness of their 

 surroundings serving the double purpose of protecting them from the pathological 

 effect of the sun's rays and of attracting the lucif ugous organisms upon which they 

 feed. This last is an important item, for upon the coast of France it has been 

 noticed that specimens of the common Antedoii hifi.ria found under rocks are much 

 larger than those found in the open, a condition, like the correlation between size 

 and depth which I have previously discussed.' mainly to be accounted for by 

 increased food supply. 



Among the crinoids there is no differentiation into a shallow-water and a deep- 

 water fauna comparable to that seen in certain other groups. The littoral or sub- 

 littoral cliaracter of tlieir original ancestors per.sists in a marked degree among 

 the present-day species, and there are but very few abyssal groups which do not 

 yet preserve the traces of the line of march by which they descended to the 

 depths. The known species belonging to eight of the 19 families are mainly littoral 

 or sublittoral, while of the remaining II, three posse.ss a minority of littoral or sub- 

 littoral species, one is known to occur witiiin 20 fathoms of the surface, and two 

 within :iO, leaving five not known except at conf^iderable depths; these five are 

 the Pentacrinitida^ (from 103 fathoms **); the Hyocrinid;ip (from 240 fathoms); 

 the Atelecrinidse (from 552 fathoms'); the Apioicrinidw (from 505 fathoms) and 

 the Phrynocrinidae (from 649 fathoms); but all of these are only slightly known, 

 and we are justified in supposing that they occur much nearer the surface than 

 present records would indicate. 



Of course the deeper down a orinoid genus or family extends the greater will 

 be its geographical range. Uniform conditions, the absence of the littoral bar- 

 riers, and the ability to attain a progressively more and more perfect circular dis- 

 persal figure, due to the absence of strong directive influences sucli as currents 

 and steadj' winds which cause the dispersal figure to become elliptical, fan-shaped, 

 or even linear, allow of a rapid dissemination in all directions. 



1 Cf. "The Recent Crinoids and their Relation to Land and Sea," Oeographical Journal. 

 DecembBr 1908, pp. 002 — 007 : also " Some Points in the Ecology of Recent Crinoids," American 

 Naturalist, vol. 42, No. 503, pp. 717—726, November I'.IOS. 



For a more detailed discussion of the ecology of recent crinoids and the factors influencing their 

 distribution, see Vid. Med., H)0!», pp. 115 - I!I4 : and Science, n. s., vol. 29. No. 747, p. 677, April 

 1909. 



i But occurring within o fathoms of the surface in the West Indies. 



S Occurring at 460 fatlioms in the West Indies. 



