110 ZOOPHYTES. 



group among the Astrseacea, yet it rests on characters of striking 

 importance (^v 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 Caryophyllidfe, where the authorities for the 

 different names of the genera adopted, are given, and the final 

 reasons for restoring the name Caryophyllia to the Cladocorse of 

 Ehrenberg. 



The genus Explanaria of Ehrenberg, made up in part of certain 

 Astrseas, and of some of Lamarck's Explanariee and Gemmiporfe, 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, /b?/r distinct genera. Its sub- 

 division, therefore, was unavoidable. The Porites spiimosa 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, Poritida3 (^ 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 Astraidcs to the Fungidce. 



( Monticularia ....)„ ■ , tt • v.i C Fungia, 

 ( Meandrina ) Manicina, Tridacophyllia i ^"""""'^ ) H^fP^toIithus S "z^'^^^^s, 



Astraja ^ ( Merulina > Agaricia ^ Polyphyllia. 



f A. orbicelltt — Echinopora, Pliyllastrtea ... ) 



