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THE VOYAGE OF H.M.S. CHALLENGER. 
oval, narrower than the trabeculae. Zooecia ovate or subrhomboidal, flattened in front ; 
very distinct in the younger portions and separated by a thin septal ridge ; walls very thin 
and transparent, surface smooth. Orifice suborbicular. Peristome thin and usually pro- 
duced on the sides and in front into a spout-like projection, 
sinuated in the middle. Labial fissure small and apparent 
only in some zooecia, being usually merged in the wide 
canalicular sinus. An angular ridge descends from the 
projecting lip and is lost on the flattened anterior surface 
of the zocecium. A small avicularium, seated on a low 
eminence, is sometimes seen a little below and to one side 
of the orifice, with an obtuse, or sometimes acute, triangular 
mandible pointing laterally or in front. Dorsal avicularia 
small and sparse, resembling the anterior or semicircular ones. In some of the fenestrse 
are boat-shaped, retentive avicularia, with a double bifid beak, and furcate membranous 
mandible, very like those in Retepora columnifera. Ocecia of large size, subglobose, with 
a trifoliate stigma, the upper limb of which usually terminates in an acuminate tubercular 
point. 
Habitat. — Station 186, off Cape York, lat. 10° 30' S., long. 142° 18' E., 8 fathoms, 
coral mud. 
Differs from Retepora philippinensis (in which species the zoarium is also constituted 
of more or less tubular or trumpet-shaped, but much wider, alveoli) in having the celliferous 
surface, as usual, on the internal face of the alveoli. And besides this, Retepora philip- 
pinensis seems in all probability to be completely unarmed. 
(17) Retepora columnifera, n. sp. (PL XXVI. fig. 5). 
Character. — Zoarium 1 inch to 2 inches or more in height, composed of numerous, 
widely expanding, flexuose, infundibuliform alveoli ; 
spreading over and affixed to foreign bodies, not by a 
common peduncular base, but by numerous solid or 
tubular calcareous columnar processes springing from 
the dorsal surface. Fenestrse oval, about the same width 
as the trabeculse, and of very uniform size. Zooecia two 
or three in the width of a trabecula, immersed and 
flattened in front ; surface entire, smooth. Orifice orbi- 
cular, with, a small shallow fissural notch in front, which 
in the youngest zooecia sometimes presents a very minute 
Generally, however, the peristome is thin, slightly 
Fio. 33. — Retepora columnifera. 
a, Operculum ; b, Columnar avicularium 
c, Fenestral avicularium. 
avicularian tubercle on one angle 
