188 THE VOYAGE OF H.M.S. CHALLENGER. 
1. Rhodarxa tenuidens, n. sp. (Pl. VIIL figs. 7-70). 
Corallum subglobose, massive, incrusting at the base, with a narrow, free edge and a 
thin, distinct epitheca. Calicles scarcely polygonal, subcircular, rather deep, about 3 mm. 
wide ; wall very porous and thin, very much thickened at the points where many cups 
meet. Septa of three cycles, the last very rudimentary, those of the first and second 
cycles almost trabeculate and raggedly spinulous below, not distinct above from the porous 
wall; pali very thin and wide, forming upright, rather broad plates, tending to fill up 
the cups, often much less elevated, but never forming thick, lobe-like pieces. 
This species makes a decided approach to Alveopora. It is distinguished from 
Rhodarxa .calicularis by the shape of its calicles, the nature of its walls and the 
characters of its pali. From Rhodarwa gracilis it differs in the size and shape of its 
calicles, and the character of its pali. Two small specimens were obtained. 
Localities.—Santa Cruz Major Island, off Samboangan, Philippines, 10 fathoms ; 
Amboina. 
2. Rhodarxa calicularis (Lamarck). 
Astrea calicularis, Lamarck, Hist. Anim. sans Vert., ii. p. 266, 1816. 
Rhodarxu calicularis, Milne-Edwards and Haime, Cor., iii. p. 183. 
A large portion of a very large, subglobose specimen was obtained. The walls are 
rather strong and uniformly thick in each calicle, but are very variable at different parts 
of the corallum ; in some places it is low and thick, marked above by the narrow septa ; 
in other places it is elevated and thinner, with the septal marking scarcely distinct. 
In the shallow calicles the pali are very thick, and rounded, very distinct, nearly filling 
up the cell; in the deeper calicles they are smaller, and much less prominent at the bottom 
of the cell. 
Locality. 
Samboangan, Philippines. 
Genus 6. Tichopora, n. gen. 
Corallum compound, porous; gemmation intercalicinal. Walls very slightly developed, 
extremely trabeculate or porous, those of adjoining calieles adherent or fused together, and 
barely distinguishable in section separating the septa. Calicles subcircular, rarely sub- 
angular, shallow. Septa well developed, of three complete cycles, equal or subequal, all 
projecting equally to meet the columella where the tertiaries join the secondaries in each 
system, perforated, trabeculate and slightly echinulate. The interseptal spaces very distinct, 
deep and regular between the perforated laminz. Columella well developed, subpapillose 
or trabeculate, largely formed by the septal ends. Pali represented by thickened, 
elevated, irregular spinules situated before the second cycle, and almost indistinguishable 
from the trabeculate ends of the columella. 
