48 MYCEDIUM. 



Dimensions slightly smaller than those of Diaseris pusilla. Both 

 species are generally found together in some ahunclance, but perfect 

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

 mens have evidently been broken and mended as the one figured in 

 Plate Y., fig. 2. Such deformities in other groups of corals have been 

 described as genera, as, for instance, Ecmesus by Phihppi, and Ilemicy- 

 athus by Seguenza. 



MYCEDIUM Oken. 

 Mycedium fragile Dana. 



This S23ecies 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 sjDCcies, 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 be 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 striie, which may be subequal, or 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 Mycedium fragile, which 

 Milne-Edwards and Haime think may be closely allied to Agaricia iin- 

 daia, 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. 



OffTortugap, in 3G and 43 fathoms. 



