No. 503] ECOLOGY OF RECENT CRINOIDS 719 



tacrinitidae above 100 fathoms is at once explained; the 

 stalked pentacrinites (Encrinus, Endoxocrinus and 

 Hypalocrinus) are animals of very considerable size; 

 besides a large crown they have a bulky stem which must 

 be nourished, and the organisms found at or near the 

 surface are not sufficient to support them; it is not until 

 the depth of approximately 100 fathoms is reached that 

 the organisms occurring in the water about them, plus the 

 cumulative effect of the rain of dead from a belt 100 

 fathoms in depth, acquires sufficient intensity to admit of 

 their existence. Incidentally, their remarkable uni- 

 formity in size is explained; for the recent pentacrinites 

 inhabit almost exclusively the 100 000 fathom belt, which 

 has just been shown to be a belt of uniform crinoid size. 

 A species of Endoxocrinus, K. iri/rille-thomsoni, and the 

 peculiar Hypalocrinus both descend to over 1,000 fathoms, 

 but both are much smaller than their relatives above the 

 600 fathom line. 



The common arctic comatulid, Heliometra glacialis 

 ( eschrichtii) occurs from east of the Kara Sea to west- 

 ward of Greenland, thence southward to off Nova Scotia ; 1 

 the southern part of the Sea of Okhotsk and the northern 

 part of the Sea of Japan are inhabited by a variety, 

 maxima, differing only in its great size. This species 

 varies greatly throughout its wide range; north of 

 Europe it is small, though rather larger around Spitz- 

 bergen; off Halifax and on the Grand Banks it reaches a 

 comparatively large size, while off the western coast of 

 Greenland it attains a diameter of 500 mm. or more, 

 reaching 700 mm. in the Okhotsk and Japan Seas. 



The west coast of Greenland abounds in fjords which 

 are continually giving off fresh water ice which floats 

 away, melting as it goes, thereby killing millions of small 

 organisms which are unable to endure a great change in 

 the salinity of the medium they inhabit; these fall to the 

 bottom and furnish an abundant supply of food for the 



