48 MYCEDIDM. 



Dimensions slightly smaller than those of Diaseris pusilla. Both 

 species are generally found together in some abundance, but perfect 

 specimens are rare, on account of their great brittleness. Many speci- 

 mens have evidently been broken and mended a< the one figured in 

 Plate V.. 6g. 2. Such deformities in other groups of corals bave been 

 described as genera, as. for instance. Ecmesus by Philippi, and Hemicy- 

 a th us by Seguenza. 



MYCEDIUM Oken. 



Mycediuni fragile Dana. 



This species was obtained in considerable quantities in the two 



localities named below. The greater number of the specimens were 

 dead, but an interesting series of young ones of all ages were obtained 

 (see Bulletin Mus. Comp. Zool.. No. 13, by Professor Agassiz). It is not 

 uncommon in less depth, though not often found on the reef. 



In looking over the materials in the Museum, for the determination 

 of this coral, it has become very apparent that a revision of the group 

 is very urgent, and that probably a large number of species, and even 

 some genera, are based on very insufficient characters and ought to be 

 united. In fact, several of the specimens obtained by me in the same 

 dredgeful. if seen separately from different localities, would unhesitat- 

 ingly lie pronounced different species; whilst being put on guard by 

 the association, a closer examination shows that the characters vary 

 considerably, even in different parts of the same corallum. Such are the 

 costal striae, which may lie subequahor alternately large and small; the 

 calicles, which may be flat or raised, isolated or in rows, columella pres- 

 ent or absent, etc. 



In this connection it may be remarked that Mycediuni fragile, which 

 Milne-Edwards and Ilaime think may be closely allied to Agaricia un- 

 da/a, has really no resemblance to that species at all. The latter is 

 found on the coast of Cuba (cabinet of Mr. R. Arango, in Havana), but 

 not in Florida, as far as I am aware. 



Off Tortuga?, in 36 and 43 fathoms. 



