BY THE KEY. J. E. TENISOX- WOODS, F.G.S., F.L.S., ETC. 125 



exactly into the caYities and lying open with their beautiful blue 

 and green tentacles exposed. On approaching them they close 

 their valves suddenly, sending up a jet of water into the air. I 

 have often had my foot caught between the valves in passing. 

 They can hold with great strength, but a knife inserted into the 

 muscle soon detaches them. It seems to me, strange how they 

 can exist on a loose block of stone, which must be moved about 

 by almost every tide. 



The large Tridacna fjigas is not met with except on the edge of 

 the reef. It is rather common, but not so much so as the former 

 species. There is some confusion about this shell, the name of 

 which is usually referred to Linnseus. But no example was found 

 in his cabinet. His definition agrees with T. squamosa, and Mr. 

 Hanley observes that the synonomy Cjuoted is incorrect and leads 

 one to suppose that Linnseus regarded all the various species of 

 Tridacna as varieties of one. Mr. Hanley seems also to think that 

 we should restrict the specific name gigas to that which is generally 

 regarded as squamosa, a change which will hardly be adopted. 

 The animals seem to vary in color, but I had too few opportunities 

 of observing to record much about them. I don't think the 

 beautiful blue and green hues occur in this species. A very 

 common bivalve shell upon the reefs is Asaph is rugosa, Lamarck. 

 Circe crocea, Lam., is pretty common. The oyster which I regard 

 as 0. cucullata. Born, is very abundant on the *' negro heads" or 

 blocks of dead coral, which project above the rest of the reef. It 

 may be that the cucullate form is an exceptional variety of the 

 common oyster referred to already as existing in such abundance 

 on the rocks at Port Douglas. 



On turning over the loose blocks of dead coral, which strew the 

 flat parts of the reef left dry at each tide, a large amount of marine 

 life is revealed. Under nearly every one, the Urchin Echinometra 

 lucunter, Leske, is found in groups, two or three together. It 

 varies very much in color. The species are brown-grey, nearly 

 white, or a delicate flesh color. They do not cling to the rock, 



