586 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



OCULINA DIFFUSA Lainank 

 (PI. XXII, tig. 149.) 



FMernul charnet<-rx. — Small colonies of this species arc m(>t witii in almiidance in the shallow 

 waters of Kingston Harlior. attached to loose objects on the sea floor; also in similar positions at 

 Bluetields Hav. J^aro'e ahorescent colonies, Id to l'^ cm. across, occur among the coral growth 

 rfithin the lIarl)or a little beyond Port Royal, and also on tlic piles of the Port Royal Dockyard. 

 In these latter places they are associated with large ccilonics of Cladoenra nrhtxc\d(i, l)oth species 

 appearing as light or dark brown arl)orescent masses. 



The column wall is much prolonged perithecall\ . a wide interval separating one polyp from 

 another, except in the neighborhood of the ape.\ of the branches, where the individuals are 

 closelv arranged. The polyps are usually raised soine distance above the general surface of the 

 colony in an ol)lii|ue manner, and are either circular oi- <>\al in sintion. They are subspirally 

 disposed, and the actual line of unit)n of c(.ntiguous colunm walls is not always determinable. 

 The external grooves corresponding with the internal attachmentof the extracalicular mesenteries 

 are at first very ])r<)nounced. l)ut tend to disappear toward the proximal termination of the polyp; 

 this actually takes i)lace oidy in the older parts of a colony. On full expansion the column 

 wall becomes raised above the edge of the theca, and is cylindrical, smooth, thin-walled, and 

 transparent. 



The tentacles are in three cycles, and usually number :i4. arranged in the formula (!, •'>, 12. 

 The members of the first and second cycles are practically equal in length, and measure 5 mm.; 

 they narrow but slightly from the proximal to the distal extremity, and the tips are colorless and 

 slightly swollen. The surface is minutely tubercular, owing to the presence of clusters of 

 nematocysts. The tentacles may be erect, spreading, or overhanging, according to the state of 

 expansion of the polyp; on full retraction they appear as mere processes of the disk. 



The disk is circular in polyps situated some distance from the apex of the branches, and alunit 

 4 mm. across on full expansion. During ordinary conditions it is depressed or flat, buttheperi- 

 stomial region may become conical on full expansion, extending l)eyond the tentacular zone for 

 some distance (tig. 14!t). Radiating ridges and grooves are presented, and the internal mesenteries 

 can be seen through: of these latter six pairs reach the stomodteum, and six pairs extend about half 

 way across the disk. Polyps occasionally bear two oral apertures on a large oral disk, sui-rounded 

 by a single sy.stem of tentacles (tissiparous gemmation). 



The mouth is slit-like, and the stomodteum shows six white longitudinal lines on each side, 

 corresponding with the attachment of the perfect mesenteries. 



The colunm wall is light or dark brown in color, tiie grooves being always darker than the 

 ridges. The tentacles and disk on full extension are a light brown, becoming much darker in 

 i-etracted examples. The lips and stoniodieum are white. The white edges of the septa and costa> 

 show through very distinctly, especially on full expansion, when the colonies as a whole assume 

 a lighter appearance. Examples obtained from shady places, as under the wharfs at Port Royal, 

 may be perfectly colorless from an aV>sence of zooxantiiellie. 



Asexual reproduction takes place by columnai' budding at the apex of the branches; tissi 

 parous gemmation also takes place occasionally. In the laboratory the polyps remain partly 

 expanded during the day, and are greatly distended at night. On retraction the column wall is 

 drawn, iris-like, within the calice, so as to cover and conceal the tentacles and mo.st of the 

 peristome. Irritation of one polyp is responded to by others inmiediately around, and retraction 

 proceeds after a short interval. 



Anatomy and Jilsfdhx/i/. —The elongated colunm wall and perithecal skeletotrophic tissues 

 inclose between them a large ccjelomic space, partitioned longitudinally by the perithecal portion 

 of the mesenteries. The superficial longitudinal chambers thus torme<l dift'er from those of most 

 corals in that they are not again partly subdivided by costal ingrowths or echimdations, the 

 outer surface of the corallum being nearly smooth; very shallow stria; above indicate the former 

 position of the perithecal mesenteries, but the intervening space is not raised into strong costa' 

 or echinulations. In retracted polyps the distal region of the column is drawn deeply within the 



