MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 555 



regions fche mesogloea of all the mesenteries becomes extremely thin, and the musculature is then 

 scarcely determinable (fig. i5). Where the mesoglcea of the mesenteries is united with that of 

 tlic column wall it forms the usual desmoidal processes for attachment to the corallum. 



Mesenterial filaments may occur on the mesenteries of all the three cycles, though as a rule 

 they are incipient on the smallest members. The filaments on the imperfect mesenteries commence 

 as high as the stomodseal region, while <>n the primary mesenteries they are developed in conti- 

 nuity with the stomodseal ectoderm as the mesenteries become free. The terminal edge of the 

 stomodseal wall is continued along the twelve primary mesenteries for some distance, and the fila- 

 ment is there cordate in transverse section, and histologically resembles the stomodseal ectoderm 

 (fig. 44); later, the filament becomes rounded like that on the incomplete mesenteries, and neina- 

 tocysts and eland cells are move numerous than above (fig. 45). As a rule the mesenterial 

 epithelium is swollen and rounded immediately behind the filament. The mesenteries are. hut 

 slightly convoluted in the proximal region, and the filaments there become crowded with large 

 oval nematocysts, which show the spiral thread very distinctly. 



The cells of the mesenterial endoderm are crowded with tine granules; and in the lower 

 regions all the cell outlines are lost, and the contents include somewhat coarse granules, which 

 stain feebly (tie-. 4.">). The endoderm cells of the column wall and of the septal invaginations 

 are also densely granular, and contain in addition numbers of the brightly-staining, .spheroidal 

 bodies referred to above. 



As the proximal region of the polyps is approached, the interseptal loculi become more and 

 more distinct from one another, and the middle is almost entirely occupied by the columellar 

 invaginations. The mesenteries disappear before the aboral region is reached, or only mere 

 rudiments remain. The skeletotrophic endoderm is very narrow above (tig. 44). but becomes 

 very broad below, and is crowded with densely granular material, all the cell outlines being lost 

 (tie'. 45). The mesoghea is indistinguishable as a distinct layer, and few traces of the skeletogenic 

 ectoderm remain. 



The corallum is penetrated throughout by a very delicate boring alga, which occupies the 

 corallar space after decalcification. It is most abundant in the superficial layers of the skeleton. 

 Spicules of boring sponges are also frequent. 



Genus PHYLLANGIA Milne Edwards and Haime." 



Polyps smooth, distinct, isolated or in close or distant groups, tissues appearing delicate and 

 transparent; perithecal continuation of gastro-ccelomic cavity and mesenteries; form short incrusting 

 corallites of various sizes. Column wall cylindrical, often prolonged basally, on retraction may nearly 

 or completely cover the disk; feeble sphincter muscle. Tentacles hexamerous, tetracyclic or incom- 

 pletely pentacyclic, entocoelic and exocoelic, long and narrow, entacmseous, tubercular, apex knobbed. 

 Stomodseal wall strongly ridged. 



Mesenteries hexamerous, largest polyps incompletely tetracyclic, six to twelve pairs complete; two 

 pairs of directives; all filamentiferous. Septal invaginations hexamerous, entocoelic and exoccelic, largest 

 polyps incompletely pentacyclic, radially short in upper region and below incompletly united centrally. 



Asexual reproduction by gemmation from the base or basal expansion of the column wall. 



Example. — Phylla/ngia americana Edw. & Haime. 



PHYLLANGIA AMERICANA Milne Edwards and Haime. 

 (PI, V, fig. 4li. ) 



External characters. — The polyps occur in small groups of a dozen or so attached to blocks 

 of coral, stones, etc., often to their under surface. In any group the polyps vary much in size. 

 Some are ~till connected by the pericalicular continuation of the column wall, others only by a 



■ i !olony incrusting, forming clusters of moderately large turbinate corallites, close or rather distant. Corallites 

 rather short. Calices circular, except where crowded, deep. Columella small or well developed, trabeculate from 

 the septal ends; with from one to three or four pillars rising from the base and uniting and joining tin- trabecules; 

 upper surface ragged or papillose. Septa well developed, numerous, unequal, some exsert, entire or minutely 

 denticulated, granular, with or without paliform lobe. Costa- usually well developed. Epitheca wanting. Endotheca 

 moderate. Basa preading, calcareous." (Duncan, 1885, p. 67.) 



