558 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



tertisxrv mesenteries. The sequence of the mesenteries in this species has been already noticed 

 (p. 4CA.) 



The individual mesenteries are characterized by the thickness of the mesoglcea, and by the 

 intricacy and depth of the plaitinos for the support of the longitudinal musculature. The 

 foldings are nearly as complicated on the incomplete mesenteries as on tiie members of the tirst 

 and second cycles, and continue thus throughout the length of the mesentery; slight variations 

 in details occur in different mesenteries. The cut ends of the til)rils of the retractor muscle are 

 very miiuite. The oblique musculature on the opposite face is strongly developed, and the 

 fibrils appear to be nearlj' vertical indirection; in the case of the complete mesenteries a very 

 distinct plaiting of the mesoglcea takes place in the stomoda^al region, thus increasing the effectual 

 surface. The cells of the mesenterial epithelium Iti the upper regions are mostly tilled with 

 deeply-staining, protoplasmic contents, and only a few clear gland cells occur. In the lower 

 regions the layei- thickens, and the contents become finely granular, the cell outlines disappearing. 



Filaments may occur on all the mesenteries, and closely recall those of Astram/ia. The 

 first part of the filament on the complete mesentaries is cordate in transverse sections, and 

 histologically resem})les the stomoda?al ectoderm, the tissue being of a similar character all 

 round. Soon, however, the filament Ijecomes circular, and nematocysts and gland cells are 

 more numerous on the anterior part of the filament; the mesenterial mesoglcea on each side also 

 becomes swollen immediately behind the filament. Still lower the filament is strongly charged 

 with large, oval, thin -waUed nematocysts. The organs are slightly convoluted below, and by no 

 means crowd the coeloniic cavity. 



The septal invaginations extend centrally but a short distance, and only toward the 

 jjroximal region are both entocadic and exoca?lic invaginations represented. The skeletotrophic 

 endoderm is much thickened below, and is densely granular, the granules of different sizes being 

 somewhat uniformly distributed throughout the layer. The lateral walls of the invaginations 

 are deeply indented, corresponding with the granules on the septal faces. 



Within the edge-zone the mesenteries are mostly incomplete on the inner side, so that the 

 perithecal chambers are but imperfectly divided. 



Genus CLADOCORA Milne Edwards and Haime." 



Polyps smooth, distant, forming bush-shaped or fasciculate colonies, free or fixed, and often 

 separated into subcolonies of from two to five polyps; perithecal continuation of the gastro-coelomic 

 cavity and mesenteries. Column wall smooth, cylindrical, elongated, on retraction may close over 

 nearly the whole of the disk. Tentacles hexamerous, entocoelic and exocoelic, tricyclic, or incompletely 

 tetracyclic, entacmseous, finely tuberculated, knobbed or rounded at end. Stomodeeal walls ridged. 



Mesenteries regularly hexamerous, dicyclic or incompletely tricyclic, six pairs complete, two pairs of 

 directives, all filamentiferous, extrusible. Septal invaginations entocoelic and exocoelic, tricyclic or 

 incompletely tetracyclic, below unite centrally (columella), giving rise to twelve separate mesenterial 

 loculi. 



Asexual reproduction by lateral columnar gemmation, rarely by fissiparous gemmation. 



Example. — Vladoconi, <irhi(sciih(. (Lesueur). 



CLADOCORA ARBUSCULA (Lesueur). 



(Pis. VI-VIII, figs. 48-63.) 



External cAaracfers. — Small bush-like colonies of this species occur in numbers in the 

 shallow waters of Kingston Harbor, and at other points around the coast, either free or attached 

 to loose pebbles or shells. Larger colonies are found in water of from three to six feet, and 

 thickly incrust the wooden piles of wharfs and buoys, or even the bottoms of boats plj^ing in the 

 harbors. 



""Colony bush-shaped or branched or fasciculate. Corallites varial)!e in length, erect, often flexuous, cj'Hn- 

 drieal, and free laterally. Calices circular and shallow. Columella well develope<l. Septa exsert, subequal, rounded, 

 and finely dentated and granulated laterally. Pali exist before all the cycles except the last. Wall compact, 

 moderately thick. Cost;e simple, granular, or finely echinulate, straight. An incomplete epitheca, which often gives 

 rise to horizontal collarettes, may extend from one corallite to another. Endotheca scanty. Gemmation lateral and 

 often in pairs from the same height on the stem." (Duncan, 188.5, p. 70.) 



