ON THE ' CHALLENGES' SPECIES OE CELLEPOBA. 341 



obtained in a similar manner from Chlorococcum. Both contain 

 the six different-coloured substances usually, if not invariably, 

 met with in green algae and in plants of higher organization, but 

 in different relative proportion. The most striking fact was, that 

 the variety of chlorophyll which I have named " yellow chloro - 

 phyll," characterized by a spectrum very different from that of 

 the more abundant " blue chlorophyll," exists in a much larger 

 relative amount than in plants of high organization, and even in 

 larger amount than in other green algae which I have examined, 

 but perhaps not in larger than might very well occur in minute 

 green algae growing in damp tropical woods. On the contrary, 

 what I have called " orange xanthophyll " occurs in smaller 

 amount in the algae from the hair than in Chlorococcum. I sub- 

 join comparative analyses, which must be looked upon as only 

 approximate. They, however, suffice to show most clearly that 

 the green colour of the hair of Sloths is due to the presence of 

 precisely the same colouring-matters as those found in green 

 algae, the difference being no greater than what may be due to 

 small differences in conditions. 



Chlorococcum. Sloth's hair. 



Blue chlorophyll 48 53 



Yellow „ 10 17 



Xanthophyll 16 17 



Yellow xanthophyll ..... . 16 8 



Orange ,, 6 1 



Lichnoxanthine ........ 4 4 



100 100 



Descriptive Catalogue of the Species of Cellepora collected on 

 the ' Challenger ' Expedition. By George Busk, E.B.S., 

 E.L.S. 



[Published by permission of the Lords Commissioners of the Treasury.] 



[Read May 5, 1881.] 



The number of species here referred to the genus Cellepora is 

 about 26 or 27. 



Of these— 



1. The North- Atlantic region yielded three, from depths vary- 

 ing from 51 to 450 fathoms. 



