INTRODUCTION. 
ON THE REEF-CORALS DESCRIBED. 
The Reef-Corals here described belong almost entirely to the Reef Madreporaria ; the 
remainder consisting of a few Millepores. With the more distinctive reef-forms have 
been included, for the sake of completeness, a few other species which were either dredged 
in rather deep water or were obtained from localities where no reefs existed. The term 
Reef-Coral, it must be confessed, is becoming rather vague in its signification ; since a 
true reef-building species may be found either in its reef-forming position, or in quite 
deep water, or in shallow water where no reefs are found. And while on the one hand 
many genera are characteristic of shallow water and the reef fauna, or of the deep sea, 
yet there are, on the other hand, many which are common to both ; and it is probable 
that extended investigation will increase the number of these at the expense of the 
former. 
The collection of Reef-Corals made was a large and an important one, there being 
representatives of two hundred and ninety-three species, referable to sixty-nine genera ; 
and many of the species are represented by series of specimens which often present a 
considerable degree of variation. 
The new species amount to one-fourth of the total number of species obtained, a 
result that is scarcely to be wondered at, considering the little that is known of the Corals 
of the vast number of Pacific and Indo-Pacific Islands. Of the seventy-three new species, 
seventy-one were obtained in the Pacific, and two in the Atlantic ; and this illustrates 
fairly well the comparative knowledge that we have of the two chief coral regions. 
Of the sixty-nine genera represented in the collection, eight are new, the specimens 
on which they were founded being all obtained from the Pacific—a fact that is again 
extremely suggestive as to our want of knowledge of the coral fauna of that immense region. 
It is perhaps advisable to notify here that in the distributional section, as well as in 
the above statements, the terms “ new species” and “new genera” are applied to all 
forms made known by the Challenger, independently of the fact that some of these forms 
have been already described in a preliminary notice of the Challenger Reef-Corals, of 
which Part I. alone was published—the remainder being suppressed, as it was expected 
at that time that the Report would speedily be ready for the press. 
