56 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 24,
ramea, is often dredged up off Madeira, and in deep water off Cadiz.
A second species is found in the Gulf of Gascony.
Amphihelia oculata, Linnaeus, is found at great depths in the Mediterranean Sea and in the Atlantic south of the Faroe Islands; and there is a species in the Australian seas. Coenocyathus and Cladocora have species amongst the deep-sea Mediterranean forms; and a species of this last genus is found off Madeira.
There are some genera which are characterized by a budding from an expansion of the base of the coral, or which throw out stolons. Astrangia astroeiformis is a type of this family; and it is a moderately deep-water species off the eastern coast of the United States, north of the reef area.
Another form, Cylicia tenella, Dana, occurs in deep water off the south-eastern coast of Africa, and also near Australia; and allied species are found off the New-Zealand and Australian coasts.
There is a facies peculiar to these compound deep-sea corals, produced by their method of budding and growth, and by the absence of cellular coenenchyma. When a collection of them is placed by the side of a series of specimens of reef-making corals, the distinction is very evident.
The habitats of these deep-sea species are rarely, if ever, invaded by the true reef forms*.
III. Exceptions.
There are deep-sea species of the genus Stylaster, Gray, (Allopora, Dana). Thus, Stylaster flabelliformis, Lamarck, sp., was found at a depth of 160 fathoms off the Isle de Bourbon. A closely allied species lives in deep water off the coast of Norway. These corals often have a coenenchyma uniting the buds; but it is of the dense non-cellular structure which peculiarizes the family of the Oculinidae, and not of the lax tissue which, with one exception, is seen in the ordinary reef corals.
The genus Madracis, which has deep-sea species off the Isle de Bourbon and Madeira, is an exception also; but the explanation just given suits its case.
IV. Littoral Corals belonging to the Deep-sea Coral Fauna.
Corals are occasionally found between low spring-tide mark and five fathoms, on the coasts of continents and large islands. Perfectly pure sea-water, freedom from muddy sediment and fresh water, a rocky bottom, and tolerably deep water close by appear necessary for their existence; and as these conditions are not to be found everywhere, the littoral corals are scarce. Vast tracts of the deep sea may be tolerably coralliferous, yet the nearest coasts are sparsely tenanted by a stunted coral fauna.
Considering the evidence which has been accumulating for years respecting the abundance of deep-sea Madreporaria in some parts of the Mediterranean and the Western seas of Europe already men-
- Count de Pourtales, Bull. Mus. Harvard Coll. nos. 6 and 7. The Stylasteres,
Errinoe, Crypthelioe, Haplophyllioce, and Thecopsammioe, &c. described by him are deep-sea dwellers in and near a reef area.
