NARRATIVE OF THE CRUISE. 



201 



ambulacrum is immensely developed, its suckers are of a gigantic size, entirely out of 

 proportion to the rudimentary ones of the paired ambulacra. 



"The colouring of the majority of the deep-sea species is a dark violet; those of 

 shallower waters are more brilliantly coloured, and such species as Ccelopleurw and some 

 of the Salenice are perhaps among the most beautiful and strikingly marked Echini." 



The bathymetrical distribution of the Sea-urchins and their relationship to the 

 previous Echinoid faunae are fully discussed in Mr. Agassiz's Eeport. 



St. Paul's Eocks. 



As the rocks were approached, it was noticed that the equatorial current ruuniug 

 past them, the velocity of which from observation was If miles per hour, caused a 

 considerable ripple, amounting almost to a race, on each side. These ripples united at 



Fig. 86.-H.M.S. Challenger at St. Paul's Rocks. 



a distance of about a mile to the westward, raising a confused sea, and leaving a 

 cone of comparatively smooth water, immediately to leeward of the islets. 



As the wind and current concurred in direction, the islets were circled until the ship 



(XARR CHALL. EXP. — VOL. L — 1884.) 26 



