1869. ] DUNCAN—CORAL FAUNAS OF WESTERN EUROPE. 57 
tioned, it is remarkable how few species and individuals of them 
have been discovered to be dwellers in shallow water*. It is doubt- 
ful 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 AXgean shores. Mr. Gwyn Jeffreys, Mr. Nor- 
man, and I agree that the stunted Caryophylha Smithi, of the Cornish 
and Devonshire coasts, isa variety of the deep-sea form Caryophyllia 
borealis. Balanophyllia regia, Gosse, which is found with the littoral 
Caryophylha, is closely allied to a deep-water species ; and Desmophyl- 
lum has 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. 
VY. Corats FrormiInGc REEFS OF ALL KINDS AND INHABITING THE 
LAGOONS AND SHALLOW SEAS IN CorRAL-TRACTS. 
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 in- 
crease by gemmation—the buds being usually united by a lax 
coenenchyma or by their walls,—by fissiparous growth with or with- 
out budding, and by serial growth, which is an endless repetition of 
the mesenteric lamine in definite directions. These structural pecu- 
harities enable individual polypes to grow rapidly, to form agegre- 
gations, and to combine strength with an endless power of reproduc- 
tion and repair. They enable the fragile-looking reef-builders to 
withstand the full force of the waves, and they promote the forma- 
tion 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 repro- 
duction and growth distinguishes them from the corals of the deep 
seas out of the range of reef areas, which have been already noticed. 
VI. Excrprions. 
Reef species straggle into the littoral tracts of continents near reef 
areas. Thus a Pocillopora of the Red Sea is common in 2 fathoms 
* See Gosse, ‘ Actinologia Britannica,’ for information concerning the littoral 
and deep-sea corals of our area. 
t+ Darwin, Coral Reefs. 
