22 MADREPORARIA. 
stomodum, and is situated between a pair of directive mesenteries. This condition is, 
however, not characteristic of the genus (cf. p. 10). 
Further information regarding the structure of the polyps and the relation of the soft 
tissues to the skeleton will be found on p. 14. 
With the exception of the peculiar mode of colony-formation, first clearly recognized by 
Ehrenberg, none of the characters hitherto included in the definition of the genus are 
absolutely constant throughout or confined to it. 
Synopsis of the Subgenera. 
Diviston I.—Madrepore with cylindrical axial corallites, which project to a greater or less extent 
at the apex of each division of the corallum; wall usually very porous, margin plane, 
exterior more or less distinctly striate or rugose. 
. Corallum usually arborescent. Axial corallites 2°5 mm. diameter or 
over, with relatively thin wall and 12 septa, the primaries being subequal. 
Radial corallites usually with a distinct star of 12 septa ...........- EvMapRepora, p. 23. 
2. Corallum more or less complanate. The second cycle of septa is absent or 
imperfectly developed even in axial corallites. The majority of the 
radial corallites are usually immersed or subimmersed; the more promi- 
nent ones have the wall acuminate .................---++-e00---- Oponrocyatuts, p. 66. 
3. Corallam usually cespitose or corymbose. Branchlets more or less 
distinctly spiciform. A second cycle of septa occurs in axial corallites. 
Radial corallites witn not more than the inner third of the wall 
TMEV OLODE Mc cquetalves seve instal ejeieicy says Welt ea MOTs eee ae Porysracuys, p. 73. 
4. Corallum usually corymbose or prostrate. Radial corallites evenly dis- 
tributed, scale-like, very spreading, giving a catkin-like appearance to 
the branchlets. ‘The outer directive septum of radial corallites is usually 
beuerdevelopedithan) the others ee. erie rr iid eee eerie clerics Lepmocyaruts, p. 115. 
Diviston I].—Madrepore in which the axial corallites are stout, thick-walled, often hemispherical, 
not exsert at the margin, or only slightly so ; wall dense, rarely striate. 
1. Corallum consisting of massive plates, the upper border of which is 
occupied by numerous axial corallites, which are slightly exsert and 
havea roundedimareine eevee + ata: annie ate Aoecee vis cei ale ORR Oe eRe Tsopora, p. 131. 
2. Corallum cespitose, corymbose, or bushy. Branchlets blunt at the apex. 
Axial corallites relatively broad, hemispherical, or slightly exsert at the 
TRAN eet ao PEO Oes. 0 5100.0 0.6 oa OM IO DERE U oe BU aa DOSS Ome Tytopora, p. 135. 
_ 
Diviston I1I.—Axial corallites relatively slender, conical or cylindrical, in the latter case of con- 
siderable length ; wall always dense. Many of the radial corallites resemble the axial ones in 
form. 
1. Corallum differing chiefly from that of Tylopora in having more slender 
apices to the branchlets and relatively small conical axial corallites .... Conocyaruus, p. 160. 
2. Axial corallites cylindrical, the prominent portion not usually longer than 
broad; wall thick and dense, margin rounded. A second cycle of septa 
IS (PLEBENE: =: w/s1h ey Mme teaesceists aes heel reid eo eto alee eee Ruaspocyaruts, p. 173. 
