GENERAL INTRODUCTION. 
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a 
and my suspicions that it belonged to the HypRorps were confirmed by the examination 
of the remarkably rich haul of StyLasTertD# obtained on the homeward voyage off the 
mouth of the Rio de la Plata. 
In the Hydroid corals of Hyprocoratiin® the hard skeleton appears to be developed 
from the ectoderm, whereas in the Anthozoan corals, both Aleyonarian and Madreporarian, 
it is not so produced. It seems necessary, therefore, that the term ‘‘corallum” should not 
be applied to the hard skeletons of both forms alike, since the skeletons in the Hydroid 
and Madreporarian corals can scarcely be considered homologous. I have, therefore, 
applied the term “ccenosteum” to the hard skeleton of the Hydrocorallinz, retaining 
the old term “corallum” for that of the Anthozoan corals, whether Alcyonarian or 
Madreporarian. 
The present memoir is divided into three parts. The first part treats of the 
HypRocoRALLine®, giving an account of the structure of the MILLEporipa# and 
STYLASTERID-®, and a list of all known species of SryLasTERID&, together with descrip- 
tions of the species obtained by H.M.S. Challenger. The second part describes the 
anatomy of Heliopora cerulea and of a species of Sarcophyton, and contains a discussion 
on the fossil corals which were probably allied to Heliopora. The third part deals with 
the Mapreporarta dredged in the deep sea. It comprises a list of all the species 
dredged, with descriptions of new forms, and some account of the anatomy of the soft 
tissues of certain species, and a table showing the depths to which all known genera of 
deep-sea corals are as yet known to range. The literature relating to the matter treated 
of is shortly discussed in each part separately. 
