572 MEMOIRS OF THE >sATlo:sAL ACADEMY OF SCIENCES. 



Tlio >;kcletotr<)phic tissues present no exceptional charactor; the endoderm is a delicate layer 

 tliroiiuhout. increasing in tliiclvness and vacuolization in the proximal regions; the gland cells 

 are practically all of the clear variety, and zooxanthellfe appear lait sparingly. The layer is 

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



The pol\'ps are iiermaphrodite: ova and sperniaria may he liorne in close contiguity bv the 

 same mesentery, though more often they are on separate mesenteries. Occasionallj' a mesenterj', 

 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 

 Bluetields. during the month of November. Larvae were also liberated from colonies collected 

 in April, while other colonies contained neai'ly 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 sing-le disk; g-astro-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 exoccelic, stem knobbed or 

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



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

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



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



Example. — Divluicwnia »i<>kem Edw. and Haime. 



niCIIOOCENIA stores: Milne Edwards and Haime. 

 (PI. XVI, figs. 117-120.) 



External chiiracten. — 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 diifers 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 scarcelj' project 

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

 erably in magnitude and form. The largest ai'e 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 H mm. Sometimes only one oral aperture occurs on a disk, 

 but often two or more are present. The two or three small colonies a\-ailable 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 arc indistinguishable. 



The column wall is strongly ridged and grooved in the reti'acted 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 are both entoctjelic and 

 exoctelic. 



The disk shows feeV>le radiating ridges and furrows, and upon retraction is much depressed 

 within the calicc The mouth is elongated and remains partly open; the lips are thickened and 

 protrude slightly. The stomodieal wall is thrown into deep ridges and furrows, the number 

 vaiying 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 



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

 numerous low caliees, some circular in outline, others united in short series. Coluiiiella small, sublamellar, or 

 subi)apillary. Septa well developed, entire, usually exsert. Pali before most of the septa. Costic rather large, 

 spinulose, and merging into the granular, dense, and highly developed intercalicular ccenenchynia, and they are 

 seen to the base. Epitheca rudimentary. Endotheca exists. Increase by fissiparity and upward growth, 

 accompanied by ccenenchymal develojiment." (Duncan, 188.5, p. 99.) 



