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1869.] tioned, it is remarkable how few species and individuals of them have been discovered to be dwellers in shallow water. It is doubtful whether any of the littoral corals now under consideration are specifically distinct from those of the neighbouring deep water.

Edward Forbes found the deep-sea Mediterranean Cladocora in shallow water on the AEgean shores. Mr. Gwyn Jeffreys, Mr. Norman, and I agree that the stunted Caryophyllia Smithii, of the Cornish and Devonshire coasts, is a variety of the deep-sea form Caryophyllia borealis. Balanophyllia regia, Gosse, which is found with the littoral Caryophyllia, is closely allied to a deep-water species; and Desmophyllumhas a littoral species very closely allied to the Mediterranean kinds.

The littoral simple corals are usually very small and stunted, and generally have broad bases, which are attached to stones or shells.

The bulk of the species of Madreporaria are included amongst these; and the reef-builders may be recognized, for the most part, by their peculiar construction. Simple corals are rare, belong to different genera and families from those which are typical of the deep-sea fauna already noticed, and usually have a very well developed system of endothecal structures, which enable the polypes to grow rapidly.

The rest of the fauna is composed of compound corals, which increase by gemmation—the buds being usually united by a lax coenenchyma or by their walls,—by fissiparous growth with or without budding, and by serial growth, which is an endless repetition of the mesenteric laminae in definite directions. These structural peculiarities enable individual polypes to grow rapidly, to form aggregations, and to combine strength with an endless power of reproduction and repair. They enable the fragile-looking reef-builders to withstand the full force of the waves, and they promote the formation of coral limestone, after the death of the polypes, in consequence of the porous nature of the coenenchyma. Moreover the methods of growth enable the reef, lagoon, and shallow-sea forms to carry out their technology in nature rapidly and surely.

It is not intended to describe reefs in this communication; for the information concerning them and the coral-seas can readily be obtained from the original source. It must suffice to assert that many families of the Madreporaria contribute to the formation of reefs, and that there are species peculiar to different portions of the structures as well as to different depths in the lagoons and shallows. But they all have a general resemblance, and their method of reproduction and growth distinguishes them from the corals of the deep seas out of the range of reef areas, which have been already noticed.

Reef species straggle into the littoral tracts of continents near reef areas. Thus a Pocillopora of the Red Sea is common in 2 fathoms