182 MU. CYlRTL CROSSLAND ON THE [Mar. 7, 



(5) Echinoderms. — Boring Echinids {Echinometra stbhangtdaris) 

 occvii- all I'ound the coasts in enormous numbers, in shallow pools 

 of the shoi-e-platform ; the holes ai-e generally diilled as near 

 togethei- as is possible. Just below the steep inci-ustation-belt 

 they occur again in the same pi'o fusion, but in the belt itself are 

 much rarer, except wheie it is horizontal. It is very remarkable 

 that this form produces equally conspicuous effects upon rock of 

 all degrees of hardness, whethei- nullipore, coral, sandstone, or the 

 very hard black basaltic rock. 



But the total i-esult of their desti-uctive action is small, e. g. on 

 sandstone of the St. Vincent reef amounting to the deepening of 

 shallow pools by three or four inches. Indeed in many cases the 

 Echinid merely takes advantage of the peculiar " potholed " forms 

 the calcareous rocks assume under the influence of the sea and 

 does no drilling at all. In any case as soon as shelter is obtained 

 drilling- operations cease, and naturally sheltered crevices show 

 feeble, merely adaptive traces of this action. On exposed surfaces 

 as soon as the recess is made deep enough for shelter the action 

 ceases, though several generations of Echini occupy the same place, 

 as is shown by the fact that the size of the hole has often no 

 relation to that of its occupant, full-grown Echini frequently 

 occupying extremely shallow depi'essions and in other cases a 

 young specimen, an inch or so across, being in possession of a 

 full-sized hole, 3 inches in diameter and depth. 



But on growing Coral the action is more impoitant. Whenever 

 a colony comes to overhang a burrow it is eaten away and this 

 portion killed, as though semicircular canals had been gouged out 

 in a line with the edge of the burrow beneath. In this way pools 

 which would be full of coral possess but stunted remnants, and 

 the extent of coral-growth on these coasts is veiy greatly reduced. 



It should be noted that these are not the only borers the instincts 

 of which may be satisfied by an accidental crevice. I have found 

 even so highly specialised a borer as the Polychaete Eunice 

 sicilieiisis inhabiting natural crevices in the nullipore and Serpulid 

 combination. 



5. The St. Vincent Fringing-Reef. 



Although ti'ue " coral-reefs " ai-e absent from these seas, a 

 remarkable simulacrum of a nullipore fringing-reef exists immedi- 

 ately to the south of the town of St. Vincent. The Admiralty 

 chart gives a much larger structure than that at pi'esent in 

 existence. In fact, there have been two distinct though perfectly 

 similar reefs, the northern and broader having been now com- 

 pletely removed to make room for the piers &c, of the Coaling 

 Companies. The two I'eefs were separated by lava rock at the 

 base of a volcanic hill, 100 feet high, on the shore, the importance 

 of which will appear later. 



The surface of the reef is at a level of from one to two feet 

 aboA^e that of lowest tides, on the whole flat, with shallow pools, 



