382 BULLETIN OF THE 



which preceded. This mode of enlargement of the communities ohtains 

 really in later periods of their growth; but it is not in that way that 

 the foundation of the community is laid. Astrcea annularis, the most 

 common species among the Madreporariaus of Florida, exhibits the for- 

 mation of these stocks very plainly. The vast number of young stocks 

 of this species which I have collected in every stage of growth leaves no 

 doubt upon the subject. A simple individual Polyp spreads by the 

 elongation of its radiating partition, Mycediu in-like, in every direction, 

 giving rise at appropriate distances to new centres or individuals 

 around the first ; and this goes on, without a marked vertical enlarge- 

 ment of the new individuals, until the community has acquired a diameter 

 of several inches ; just as in the cases of Mycedium, Agaricia, and Sider- 

 astrcea. The appearance of this spreading margin of the youug 

 Astrasa stock is so like that of a spreading Fungian, that, if detached 

 from the well-defined circular individuals occupying the centre of the 

 disk, it would unhesitatingly be taken for a fragment of a Fungian. 

 It is only at a later time that in Astrcea annularis the members of the 

 community are developed in a vertical direction, and the community as 

 a whole is enlarged by the interpolation of new individuals, to assume 

 the form of a hemispheric mass. I have observed the same mode of 

 growth in Astrcea cavernosa, in Manicinia, in Symphyttia, in Favia, in 

 CvlpophyUia and in Meandrina. Of Manicina I possess a series of 

 young still exhibiting their Turbinolian characteristics, with interseptal 

 chambers open from top to bottom, and without a trace of traverses. 

 The corals with undulating and meandering trenches arise also, like 

 compound Fungians and compound circular Astrseans, from single in- 

 dividuals, with circular outlines spreading from the margin, after the 

 fashion of Fungians, just as much as Astra?a proper. The peculiarities 

 exhibited by each type cannot well be described without figures ; I 

 shall therefore not attempt here a detailed report of all the facts 

 I have observed, reserving a fuller statement for a special memoir. 

 But Mm mi rim i exhibits some features so particularly intere-ting 

 that I cannot pass on without giving some more special account of 

 them. When the young spreading Meandrina has acquired the dimen- 

 sions of aboul half an inch, still plainly exhibiting Fungian character- 

 istics, it- marginal extension gives rise to the formation of iMilated 

 clusters of rising radiating partitions, which stand distinct from one 

 another, just like the characteristic hills of a Hydnophora : in fact, the 



