MADREPOEA. 27 



appears to me to belong here. It consists of only the apical portion of a colony in which 

 the branches are slender and the majority of the radial corallites are tubular. A small 

 specimen of this form in the Berlin Museum bears the name Porites cristata, Ehrb., on the 

 label. No species appears^ however, to have been described by Ehrenberg under that name. 



Other specimens have thicker branches and are more arborescent in habit, and lead up 

 to the forma cervicornis. 



C. Forma cervicornis. 



Corallum erect, arborescent, frequently 60 cm. or more in height and 30 to 70 cm. broad. 

 Base sometimes a simple dilatation of the stem, at others broad and incrusting. In certain 

 specimens the whole colony forms an incrustation over dead coral, and only the distal 

 branches are entirely produced by the new colony. In such specimens it frequently happens 

 that the incrusted branches are blunt at the apex, and no axial corallite is distinguishable. 

 At a later period, when independent growth commences, one of the corallites, situated 

 about the centre of the rounded apex, increases gradually in size, and becomes the axial 

 corallite of the branch in its further extension. This accounts to a great extent for the 

 marked variation in size of the axial corallites, and forms an important link between this 

 variety and forma palmata. Stem 2 to 4 cm. thick, or, in exceptional cases, 5 cm. 

 Branches elongate and spreading, sometimes almost at right angles, but different specimens 

 vary considerably in this respect; they are round, gradually tapering, TS to 2, rarely 4 cm. 

 thick, usually not much divided, and sometimes simple when 19 cm. in length. Near the 

 periphery of the colony a few short branchlets occur, 1'5 to 3*5 cm. long and about 1 cm. 

 thick ; frequently two or three occur close together. Axial corallites cylindrical, normally 

 4 to 5 mm. thick, and frequently 6 to 8 mm. exsert ; wall thick and very porous, strongly 

 striate externally. Primary septa well-developed and subequal, second cycle more or less 

 prominent. It also appears from Agassiz's figures (' Florida Reefs,' pi. xviii.) that in the 

 axial polyp the cycles of large and small tentacles are very distinct, but the difference is not 

 so marked in the radial polyps. Radial corallites rather crowded and more or less appressed 

 near the apex of a branch, but more spreading and usually a little more distant below, from 

 13 to 16 in 5 cm. Immersed corallites are rare, excepting in the basal parts of the 

 colony. The form is chiefly tubo-nariform in the younger parts and nariform below, where 

 the thickening, of the sclerenchyma has covered the tubular base; length 2 to 5 mm., diameter 

 1-7 to 2'7 mm., but adjoining corallites are subequal, and the longest ones are usually situated 

 near the apex. In some specimens nearly all the radial corallites are nariform, in others a 

 few have a rather elongate lip. Wall firm and a little thickened, but quite porous, becoming 

 much thickened and even keeled with age. The directive septa are broad, the others usually 

 narrow. Corallum porous, surface spongy and echinulate; wall strongly striate and 

 echinulate. 



A specimen from Hayti, in the Strassburg Museum, differs from the majority of 

 specimens which have come under my notice in having the whole corallum, including the 



