574 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Genus ISOPHYLLIA Milne Edwards and Haime." 



Polyps large, coarsely and irregularly verrucose, tissues dense and strongly pigmented; one or 

 many orai apertures on a single disk, which is often prolonged linearly; give rise to massive fixed 

 colonies, convex or subplanate above. Gastro-coelomic cavity and mesenteries prolonged perithecally 

 around the margin of the colony. Column wall occasionally distinct, generally united with that of 

 the contiguous rows along a common narrow or broad thecal edge; on retraction may fold over 

 the tentacles and lateral portions of the disk. Sphincter muscle well developed. Tentacles approxi- 

 mately dicyclic, entocoelic and exocoelic, introvertible, short, stem with circularly arranged urticating 

 areas, rounded or knobbed terminally. Stoinodasal walls deeply ridged. 



Mesenteries irregularly dicyclic, in irregular stomodasal systems; all filamentiferous; directives 

 absent; mesenteries and filaments partly protrusible. Septal invaginations mainly entoccelic; interseptal 

 chambers not wholly distinct below. 



Asexual reproduction by partial or complete fission. 



Example. — Isophyllia dipsacea Dana. 



ISOPHYLLIA DIPSACEA Dana. 

 (Pis. XVII, XVIII, figs. 121-128.) 



External characters. — The colonies are convex or Hat, massive, non-incrusting, attached l>y 

 a narrow base, and subcircular or irregular in outline. The specimens met with often attain a 

 diameter of 5 or 6 inches, and occur on the reefs from a depth of 3 or 4 feet downward. The 

 discal areas are mostly continuous, but in places the column wall extends across, and completely 

 separates one discal system from another. The systems are arranged in a somewhat radiating 

 manner, especially in young colonies, but the disposition becomes more irregular in older 

 specimens. The separate discal systems vary much in their extent; sometimes a simple polyp 

 occurs with only a single oral aperture, but in most cases the disks become meandering as a 

 result of imperfect fission. Under ordinary conditions of retraction, the distal thickened margin 

 of the columnar areas extends more than half-way clown the calice, and becomes overfolded so as 

 to cover the tentacles and peripheral portions of the disk. The column wall extends over the 

 margin of the colony for nearly a centimeter, inclosing continuations of the gastro-coelomic 

 cavity and mesenteries. 



The superficial tissues as a whole appear very coarse, and are dark and non-transpavent, 

 causing the colonies to stand out prominently against the white coral sand of the sea floor, or 

 against other lighter corals. Examined closely, the surface of both the column and disk presents 

 a finely granular appearance, which on microscopic investigation is shown to be due to aggre- 

 gations of granules within the ectodermal cells. 



The line of union of contiguous columnar areas is clearly indicated by a shallow groove, which 

 is smoother and less densely pigmented. The surface of the column generally is very irregular 

 under ordinary retraction, and the septal spines and teeth give rise to rows of protuberances, 

 varying in size and height, and only approximately representing larger and smaller alternating 

 rows. They appear as verruca- on the retracted polyps, and are scarcely noticeable on full 

 distention. Owing to the thickness and opacity of the tissues, the lines of attachment of the 

 internal mesenteries are ordinarily not visible externally. 



On retraction the tentacles are hidden under the partly overhanging columnar areas, and on 

 expansion they appear in two alternating rows, the outer a little smaller than the inner. They 

 are short, either narrow and columnar, or swollen and tapering, with an opaque white apex, 

 either in the form of a distinct knob or as a mere lighter area. The surface of the stem hears 

 oval or irregularly shaped nematocyst thickenings, with the long axis arranged circularly; 

 otherwise the walls are nearly colorless and transparent. 



" "The colony is massive, convex above or subplanate. The corallites are in short or long linear series, which 

 are united by their walls completely, or having a slight groove between them, or united below by the walls and 

 close to tin- surface by costse and exotheca. Calicular centres distinct in the series. Columella spongy. Septa 

 numerous, much spined. Collines stout, tall, may be furrowed on the top. Endotheca abundant " (Symphyttia, 

 Duncan, 1885, p. 91.) 



