572 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



The skeletotrophic tissues present no exceptional character; the endoderm is a delicate layer 

 throughout, increasing in thickness and vacuolization in the proximal regions; the gland cells 

 are practically all of the clear variety, and zooxanthellse appear but sparingly. The layer is 

 sharply indented in places, corresponding with the echinulations on the face of the septa 



The polyps are hermaphrodite: ova and spermaria may be borne in close contiguity by the 

 same mesentery, though more often they are on separate mesenteries. Occasionally a mesentery, 

 in section, will contain only a single large ovum. 



Gonads, along with far advanced larva', were present in all the polyps of several colonies at 

 Bluefields, during the month of November. Larva' were also liberated from colonies collected 

 in April, while other colonies contained nearly ripe eggs. 



Genus DICHOCCENIA Milne Edwards and Haime.'' 



Polyps verrucose, close or more distant, the line of separation distinct or absent, very variable in 

 size and outline, one, two, or many oral apertures on a single disk; gastro-coelomic cavity and 

 mesenteries prolonged perithecally; form massive, pedunculate, hemispherical, or plane colonies. 

 Column cylindrical, oval or irregular, on retraction folding- over the tentacles and periphery of the disk, 

 no sphincter muscle. Tentacles irregularly multicyclic, entocoelic and exocoelic, stem knobbed or 

 rounded terminally. Stomodaeal ridges well developed, very variable in number. 



Mesenteries irregularly multicyclic, all filamentiferous, directives absent. Septal invaginations 

 mainly entoccelic, but in places exoccelic, not wholly uniting centrally. 



Asexual reproduction by stomodaeal fission, which may be complete or incomplete. 



Example. — DicJwcmnia stok&si Edw. and Haime. 



DICHOCCENIA STOKESI Milne Edwarda and Haime. 

 (PI. XVI, tigs. 11 7-1 I'll.) 



External characters. — Colonies of this species have been obtained at a depth of 10 or 12 

 fathoms in attempts to trawl over the Pedro Banks. It is not met with in shallower water, so 

 that its habitat differs somewhat from that of the other species here described, which have all 

 been obtained at wading depths. 



The polyps have been examined only in the retracted condition, when they scarcely project 

 above the general surface of the colony. The individual polyps or polypal systems vary consid- 

 erably in magnitude and form. The largest are oval, or narrow and elongated, the smallest 

 circular or subtriangular; the long diameter may vary from 1 cm. to several centimeters, and 

 the short diameter is usually only '■'• mm. Sometimes only one oral aperture occurs on a disk, 

 but often two or more are present. The two or three small colonies available for study do 

 not exhibit the meandering* discal systems such as are figured in "Florida Reefs", PI. X. 

 The external lines of division between the individual polyps are mostly well marked, and usually 

 subpentagonal in outline; in some instances, however, they are indistinguishable. 



The column wall is strongly ridged and grooved in the retracted state, the ridges exhibiting 

 small mammiform verruca', corresponding with the echinulations along the costal edges. In 

 retracted polyps the upper part of the column is partly overdrawn, and the greater portion of 

 the disk remains visible. 



The tentacles appear as if arranged in two alternating cycles, and arc both entocoelic and 

 exoccelic. 



The disk shows feeble radiating ridges and furrows, and upon retraction is much depressed 

 within the calice. The mouth is elongated and remains partly open: the lips arc thickened and 

 protrude slightly. The stomodaeal wall is tin-own into deep ridges and furrows, the number 

 varying much in different polyps, according to the size of the oral aperture. 



Asexual reproduction takes place by fissiparity, and appears to be in most rapid progress 



a "The colony is massive, pedunculate, hemispherical, lobed, or plane, ami the large upper surface presents 

 numerous lew calices, seme circular in outline, others united in short series. Columella small, sublamellar, or 

 subpapillary. Septa well developed, entire, usually exsert. Pali before most of the septa. 0>st;e rather large, 

 spinulose, ami merging into the granular, dense, ami highly developed intercalicular ccenenchyma, ami they are 

 >'<ii tn the 1 iase. Epitheca rudimentary. Endotheca exists. Increase by fissiparity and upward growth, 

 mpanied by ccenenchymal development." (Duncan, 1885, p. 99.) 



