1900.] ME. F. P. BEDFORD ON MALAYAN ECHINODEBMS. 273 



mouths of the rivers extensive deposits of silt mixed with 

 vegetable debris occur, and here, as a rule, the reef is poorly, if at all, 

 represented ; in places, however, where the reef is nourishing its 

 distance from the shore is very variable, rarely exceeding 500 yards, 

 and the lagoon shore is of the most varied description — mangrove- 

 swamps, tracts of hard sand, or gravel may occur, or volcanic 

 rocks may come down to the water's edge and, being eroded by the 

 action of the sea, form tide-pools and crevices when the tide 

 recedes. 



Each kind of environment was found to have its own peculiar 

 Echinoid fauna, each species except the most abundant being 

 restricted to one sort of habitat in its adult condition ; and in this 

 connection it is worth noting that, although this is constant 

 throughout the district, yet in other localities, e. g., Batavia, the 

 same species will be found in a different environment. A good 

 instance of this is afforded by Diadema saxatile, which was the only 

 reef-Echinoid of the district, and was a conspicuous object among 

 the masses of coral on nearly all the reefs ; whereas at Batavia this 

 species was apparently found by Dr. Sluiter (cf. also Studer *) a 

 short distance from coral on patches of sand, Echinometra lucunter 

 being common among coral in that locality. It seems to me that, 

 by a similar change of habitat, a certain amount of isolation might 

 be caused which would enable variations in a direction favourable 

 to that environment to become normal for the particular form- 

 unit, and by a continuation of the process specific distinctions 

 might become fixed. Without some such isolation it is difficult to 

 imagine how any variations from the norm could become suffi- 

 ciently stable to be perpetuated alongside of the type, or how any 

 gradual modification could take place in the type itself 2 , since the 

 pelagic plutei that settle down in any given limited area can 

 hardly be supposed to be the offspring of adults living within that 

 same area, and there is no evidence, so far as I am aware, of 

 discontinuous variation among Echinoids likely to lead to the 

 formation of new races. 



The species of which examples were obtained number sixteen, of 

 which it may be worth remarking that four extend as far south as 

 New Zealand ; this is interesting in connection with the distribu- 

 tion of Asteroids and Holothurians, which appears to be much 

 more limited. 



Only a few Echinoids have been previously recorded from the 

 locality, but of these there are two species which we have failed to 

 find, and which are not represented in the Baffles Museum ; they are 

 Salmacis dussumieri and Rhahdocidaris bispinosa : there are 

 specimens of the latter in the British Museum collected by 

 Dr. Powell at Singapore, and 1 have satisfied myself of their 

 distinctness from Bhabdocidarls annuUfera. Only one new species 

 is described, belonging to the morphologically interesting genus 

 Asthenosoma, and we were fortunate in obtaining two young 



> T. Studer, Monatsber. d. Ak. Wiss. Berlin, 1880, p. 868. 



3 Cf. A. E. Ortmann, Grundziige d. mar. Tiergeographie, 1896, p. 31. 



