TRIBE III. MADREPORACEA. 107 
D. Thin incrusting. 
23. P. lichen. 25. P. arenacea. 
24. P. retie ulosa. 
1. PoRiTEs MORDAX [Dana). — Cespitose, alive for 3^ to 4 inches ; branches 
subsimple and somewhat compressed, below, often coalescing into a plate, 
branchlets 1^ to 2 inches long, i of an inch thick, and * to 1 inch broad, 
piano-rotund at apex, not clavate. Corallum strong and firm, with the surface 
harsh ; cells large (f of a line), deep and conical ; septum acute, scabrous. 
Plate 53, fig. 3, corallum, natural size; 3«, cell, enlarged. — Sandwich Isl- 
ands. — Exp. Exp. — Var. elongatum, plate 53, fig. 4. 
2. PoRiTES coMPRESSA [Dana). — Cespitose, alive for 1^ to 2 inches, sub- 
lamellate, and erect, coalescing below, lobed above or lobato-ramose, lobes 
compressed, i to f of an inch broad (rarely 1| inches), short (i an inch), sub- 
truncate at summit, and 3 to 4 lines thick, not at all clavate. Corallum firm; 
cells i a line broad, neatly polygonal, quite shallow, piano-conical; septa 
acute and very thin. 
Plate 53, fig. 5, corallum, natural size ; 5a, cell, enlarged; fig. 8, outline of 
same. — Sandwich Islands. — Exp. Exp, 
3. PoRiTEs CLAVARiA [ElUs,) Lamavck. — Short cespitose, alive for 2 inches ; 
branches flexuoiis, and quite stout, broad clavate, with the summits compressed 
and lobed, 1 to 2 inches broad, and i to f of an inch thick, sometimes subfla- 
bellate, very obtuse ; polyps very salient ; tentacles whitish, short, disk brown, 
margin of the mouth white. Corallum very porous, spongy at summit ; cells 
shallow, subconical or plane within, rather large (nearly f of a line broad) ; 
septa thin and acute. 
West Indies. — Ellis, Lesueur. 
4. PoRiTEs FLEXuosA [Dana). — Short cespitose, alive for 2i inches ; 
branches flexuous, divaricate, quite short, 1 to | of an inch thick, dilated at 
apex, very obtuse or subtruncate, sometimes subflabellate, 1 inch broad, and 
lobed. Corallum quite porous, spongy at apex ; cells large (nearly four-fifths 
of a line broad), shallow, flat at bottom, septa obtuse. 
Barbadoes, West Indies, 
5. PoRiTES ruRCATA [LamorcJc). — Short cespitose, alive for 1 to 14 inches, 
tortuously ramose, branches divaricate, somewhat compressed, 4 to 4 an inch 
thick, sometimes 1 inch broad, and subflabellate ; apex subtruncate, furcate or 
trifurcate. Corallum quite porous, apex rather spongy ; cells small, scarcely 
f of a line broad, a little excavate, subconical or flat at bottom ; septa thin 
and acute. 
West Indies. 
