586 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



OCULINA DIFFUSA Lamarck 



(PI. XXII, fig. 149.) 



Exit ruiil charactt rs. — Small colonies of this species arc met with in abundance in the shallow 

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

 Bluefields Bay. Large aborescent colonies. 10 to 12 cm. across, occur among the coral growth 

 within the Harbor a little beyond Port Royal, and also on the piles of the Port Royal Dockyard. 

 In these latter places they are associated with large colonies of Cladocora arbuscula, both species 

 appearing as light or dark brown arborescent masses. 



The column wall i^ much prolonged perithecally, a wide interval separating one polyp from 

 another, except in the neighborhood of the apex of the branches, where the individuals are 

 closely arranged. The polyps are usually raised some distance above the general surface of the 

 colony in an oblique manner, and are either circular or oval in section. They arc subspirally 

 disposed, and the actual line of union of contiguous column walls is not always determinable. 

 The external grooves corresponding with the internal attachment of the extracalicular mesenteries 

 are at first very pronounced, but tend to disappear toward the proximal termination of the polyp; 

 this actually takes place only 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 24. arranged in the formula •!. 6, 12. 

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

 tbev 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 (dusters 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 about 

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

 stomial region may become conical on full expansion, extending beyond 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 stomodseum, and six pairs extend about half 

 way across the disk. Polyps occasionally bear two oral apertures on a large oral disk, surrounded 

 by a single system of tentacles (fissiparous gemmation). 



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

 corresponding with the attachment of the perfect mesenteries. 



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

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

 retracted examples. The lips and stomodseum are white. The white edges of the septa and eostse 

 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 absence of zooxanthellse. 



Asexual reproduction takes place by columnar budding at the apex of the branches; ii"i 

 parous gemmation also takes place occasionally. In the laboratory tin' 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 most of the 

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

 proceeds after a short interval. 



Anatomy <nt<! histology.— The, elongated column wall and perithecal skeletotrophic tissues 

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

 of the mesenteries. The superficial longitudinal chambers thus formed differ from those of most 

 corals in that they are not again partly subdivided by costal ingrowths or echinulations, 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 eostse 

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



