MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 593 



the polyp. The org^ans occur ovei' the apparent centripetal termination of the septa, and no 

 cyclic regularity can be established (p. 429). 



The disk is small, subcircular, smooth, thin-walled, and very limited in extent. The mouth 

 is small, circular or oval in shape, sometimes with a prominent peristome. 



The general color of the colonies as a whole is a bright reddish brown, and minute, emerald 

 green circles indicate the positions of the numerous mouths. Observed with a lens the bright 

 green, peristomial color fades gradually toward the middle of the disk. Sometimes a faint 

 iridescent green extends over the whole surface of the colony. The septo-costse show through 

 the tissues as lighter lines. Occasionally the green oral coloration may be absent, or replaced 

 by a bright orange color. 



New polyps ai'ise near the margin of the colony, but from the external indications it is 

 impossible to sa_v whether l)y gemmation or lissiparity. The mesenterial arrangement, however, 

 agrees with that of other forms in which tissiparit}' is undoubted; Ortmann (1890, p. 288) places 

 the species under the division of "'Ccenenchymknospung." 



The species occurs somewhat sparingly in shady places on the coral reefs around the Port 

 Royal Cavs, from a depth of 3 to 4 feet downward. The bright, reddish brown color of the 

 colonies as a whole renders them very conspicuous against the white dead coral blocks to which 

 they are usually attached. 



Anatomy and liiffolixji/. — The outer superficial coveringof the colony is very delicate, and the 

 same remark may be made of the tissues as a whole; the column wall in sections is onlj' 0.023 mm. 

 in thickness. It forms very deep ridges and furrows, and in preserved material usually rests 

 directly upon the skeletotrophic tissues of the septal ridges (fig. 162). Mesenteries are attached 

 along the lines of depressions, but their vertical extent is very limited as they approach the 

 thecal wall, increasing toward the more central part of the polyp. Little or no histological 

 distinction separates the column wall, the tentacular zone, and the more central part of the disk, 

 while in sections the tentacles themselves are onlj' detei-minable by the occurrence of a few 

 closely arranged large nematocysts in certain swollen -regions (fig. 103). 



The ectoderm of the column wall contains numerous clear gland cells, and small nematocysts 

 occur here and there, and in some jjlaces accumulations of granular matter are found in the 

 deeper portions of the layer. The mesogloea appears as an extremely delicate supporting lamella; 

 the endoderm is also a comparatively thin layer, and its cells contain only a few zooxanthella>. 



The tentacles are represented in sections as single, slightl}' swollen batteries of nematocysts, 

 0.05 mm. across, situated over a septal ridge, and disposed at different distances from the oral 

 aperture. A weak ectodermal and endodermal musculature can be detected in connection with 

 the tentacles, though not in any other region of the outer wall. The stomoda?um is smooth all 

 around and presents no distinctive features. 



The mesenteries are delicate structures, the mesogloea being thin and the epithelial layer 

 verj' narrow. The retractor nmsculature is feeble, and is supported upon slight mesogheal 

 foldings; zooxanthellre occur but sparselj' in the endoderm. Peripherally the mesenteries have 

 only a short vertical extent, but centrally they extend nearly the full vertical height of the polyp. 



The mesenteries are irregular in number and arrangement, and, as in the case of polyps 

 reproducing by fission, directives are always absent. A transverse section through a polyp 

 immediately below the stomodsval region is represented in fig. 161, from which it is seen that 

 little regularity obtains in the relative sizes of the mesenteries, and in the alternation of larger 

 and smaller pairs; as shown in fig. IGi, from a section through the stomodteal region of another 

 polyp, a regular alternation of complete and incomplete pairs may occur. The incomplete pairs 

 as a rule vary much in size, and in places a pair may be missing, while of the complete pairs 

 some may cease their connection with the stomodfeum in advance of the others, or even one 

 moiety before the other. In one polyp all the mesenterial pairs, with one exception, were 

 united with the stomodieum, and entoccelic and exocoelic septal invaginations occurred with 

 perfect regularity. The number of complete pairs bears no suggestion of an3' hexameral 

 symmetry; seven equal pairs are present in the polyp from which fig. 164 was taken, and eight 

 pairs in another polyp. 



