MADREPORA. IAL G/ 
diameter and 1 mm. exsert in the type specimen; wall firm but not very thick, the aperture 
usually wide. Radial corallites spreading, imbricate, crowded, with the walls in contact in 
some specimens but free in others; they are gutter-shaped, thin-walled, and usually extend 
almost at right angles. In the type specimen the length is 1:25 mm., the breadth at the 
apex 1:75 to2 mm. In other specimens the length may be 15 mm. or slightly over, and the 
diameter 2 to 2°3 mm. The radial corallites gradually become reduced in length until 
towards the base of the branchlets all are immersed. On the marginal branchlets the coral- 
lites are more spreading and are not quite so crowded. Corallum porous, surface reticulato- 
echinulate, wall striato-echinulate. In Studer’s ‘ Gazelle’ specimens the axial corallites are 
usually 2°5 to 3 mm. thick, and the under surface of the corallum bears numerous spreading 
conical twigs. A fine series of specimens form part of the Sayille-Kent Collection, which 
exhibit considerable variation. Some agree closely with Studer’s specimens, others have 
more distant and more distinctly open radial corallites ; in some the corallites of the more 
central branchlets are distinctly ascending, but in others there is scarcely any difference in the 
angle of the corallites of the middle and the peripheral divisions. The axial corallites are 
provided with 12 well-developed septa; the directives are slightly broader than the other pri- 
maries. In the radial corallites often only the directive septa are recognizable, the outer one 
rather stouter and sometimes broader than the inner. In older corallites the star consists of 
a primary series of septa and a more or less complete second cycle ; all are very narrow, but 
the outer directive is a little more marked. 
Var. compacta. 
This name is proposed for a variety which recalls the appearance of WM. hebes, but the 
habit is not fruticose as in that species. The branchlets are usually shorter, stouter, and 
more crowded than in typical specimens, and the colony is either prostrate or forms small 
compact corymbose clumps. The radial corallites are short with a thickened base, and thus 
resemble those of some specimens of M. hedes rather than typical M. millepora, but the con- 
dition of the septa is the same as in typical M. millepora. 
Probably the species described and figured by Dana as M. millepora is distinct from 
Ehrenberg’s species. Unfortunately his type specimen does not appear to be preserved 
in the National Collection at Washington. The figure shows a much more open reti- 
culum than occurs in the Berlin specimens, and, what is perhaps of more importance, the 
radial corallites of the central branchlets are much smaller, more crowded, and much less 
spreading than those of the marginal divisions. I have regarded it as synonymous with my 
M. squamosa. Apparently M.-Edwards and Verrill have followed Dana in the identification 
of M. millepora, Ehrb., but this is not certain. On the other hand, M. convewa, Dana, 
approaches M. millepora, Ehrb., and may prove to be a variety of it. The points of difference 
are noted under the heading M. convera. I am inclined to refer some of the specimens 
studied by Ortmann to M. millepora rather than to M. convexa, but one of them (Indian Ocean, 
Conrad) comes nearer to var. compacta than the type. The branchlets are 8 to 10 mm. 
thick, and the radial corallites are very short, broad, open labellate, and imbricate, 2°5 to 
R 
