110 ZOOPHYTES. 
group among the Astreacea, yet it rests on characters of striking 
importance ({} 43, 78). 
111. As the characters laid down for many of the received genera 
were not drawn from a study of the animals, it has been found neces- 
sary to vary their limits, restrict, extend, divide, or unite, according 
to the facts thus ascertained. ‘These changes have been made cau- 
tiously, and no new names introduced, except after long deliberation. 
On account of the various uses of the same name, by different 
authors, it has been sometimes extremely difficult to decide on the 
one to be received and retained. The admirable principles published 
by the British Association, in 1843, have been followed in such cases. 
An instance of the difficulty alluded to, will be found illustrated in 
full under the family Caryophyllide, where the authorities for the 
different names of the genera adopted, are given, and the final 
reasons for restoring the name Caryophyllia to the Cladocore of 
Ehrenberg. 
The genus Explanaria of Ehrenberg, made up in part of certain 
Astreas, and of some of Lamarck’s Explanarie and Gemmipore, has 
been disbanded, for reasons stated under the genus. ‘The genus 
Porites, as employed by late authors, contains two distinct genera, or 
if we include fossil species, so called, fowr distinct genera. Its sub- 
division, therefore, was unavoidable. The Porites spumosa is the 
type of one of the recent genera, which I have called Manopora; the 
species are closely related to the Madrepores. ‘The Porites glomerata 
and clavata are types of the other genus (Porites), which is so 
decidedly peculiar in its characters, that it was necessary to establish 
it as the type of a separate family, Poritide ({ 40). 
Other remarks, upon the changes that have been found unavoid- 
able, will be made in the course of the following pages containing 
descriptions of the genera and species. ‘Those genera, whose places 
in the system are not determined, are placed in an Appendix. 
112. A few of the transitions among the genera are pointed out in 
the following tables : 
1. Transitions of the Astraide to the Fungide. 
Monticularia. . . . Pavoniany Fi tolith Fungia, 
Meandrina 2 Manicina, Tridacophyllia § ioe ee Zoopilus, 
Astrea a 04 Besrely 
Merulina . OO Oe 0 Polyphyllia. 
A, orbicelle—Echinopora, Phyllastrea 
