30 '-ALBATROSS" TEOPICAL PACIFIC EXPEDITIOX. 



13 fathoms. Tubipora was brought up froui deep water (742 fathoms) 

 off Marokau Island. The bathymetrical limit of the I'eef-buildiug corals 

 seems to be about 20 to 22 fathoms. 



Nowhere have I seen such extraordinary development of incrusting 

 Nullipores as on the sea edge of the shore platforms of some of the 

 Paumotu atolls, where they build up to a height often of four feet to form 

 the outer edge of what may be called a secondary barrier reef so fre- 

 quently seen along the sea reef faces of the Paumotus. Incrustation by 

 Nullipores gives the reef platform a decided peach or pinkish or orange 

 red tint in addition to that of the patches of Pocillipora growing upon the 

 very edge of the platforms.^ The whole platform thus has a very decided 

 hue, but most marked and brilliant on the raised edge of the sea face. 



The Tridacnas of the Paumotus are not more than six to eighteen inches 

 in length, — dwarfs compared to the giant species of the Queensland coast. 

 It is only when we come as far west as the Gilbert Islands that we again 

 strike the giant Tridacna, which has a special value to the natives of the 

 groups adjoining the Gilberts. They use the thick part of the shell near 

 the hinge to make mat-beaters, and the harder and tougher parts of the 

 curved part of the shells they shape into axes and knives. 



But little seems to be known regarding the reproduction of the pearl 

 oj'^ster, and thus far all attempts at planting and artificial reproduction or 

 regulation of fisheries have proved unsuccessful. Certain islands are after 

 the lapse of a couple of years thrown open again to pearl-divers, and this 

 close season has thus far proved successful in checking the destruction of the 

 pearl by overfishing. But a single season like the present one at Hikueru, 

 where the greater part of the fishing population of the Paumotus is assem- 

 bled within such narrow limits as the Hikueru atoll to collect pearl shells, 

 must be a great strain on its productive capacity. 



On pearl shells said by the natives to be six years old we found 

 growing stems of a species of Madrepora and one of Allopora, each fully 

 eight inches in length. 



The Echinoderms we collected in the Paumotus all belong to genera and 

 species having a wide geographical range, the majority extending from the 



' See Dana's description of this on tlie Ahe platform, loc. oil., p. '201. 



