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THE VOYAGE OF H.M.S. CHALLENGER. 
(b) Unilaminar, erect or crustaceous unattached (hemescharan). 
(3) Mucronella quadrata, n. sp. (PL XVIII. fig. 5, and PI. XVII. fig. 8). 
Character. — Zoarium closely investing a branch of coral but not attached to its 
surface ; of a white colour. Zooecia very uniformly serial, rectangular and almost square, 
separated by very thin septal ridges. Surface convex, uniformly and closely punctate, 
wall thick, opaque. Orifice orbicular, mucronate, with an acute, curved, internal 
articular denticle on each side. Occasionally, but very rarely, a large intercalated 
immersed avieularium with a spoon-bill shaped mandible. Dorsal surface entire, smooth, 
porcellanous. 
Habitat. — Station 172, off Nukalofa, Tongatabu, 18 fathoms, coral mud. 
(4) Mucronella delicatula, n. sp. (PL XVIII. fig. 2). 
Character. — Zoarium tubular, free. Zooecia serial, subquadrangular in front, quite 
square behind, separated by very thin septal ridges. Anterior surface flattened, surface 
finely granular with a single row of pores round the border. Orifice orbicular, peristome 
thin, entire ; a rather wide expanded median mucro, and a very minute, rather obtuse, 
articular tooth on each side within the border of the orifice. On some of the zooecia, 
a sessile avieularium on one side of the body with a triangular mandible pointing down- 
wards. Ooecia unknown. 
Habitat . — Off Honoruru, Sandwich Islands, 20 to 40 fathoms. 
The orifice in this species is truly orbicular in all stages of growth, and the peristome 
does not appear to undergo any secondary development. The mucro though within the 
border of the orifice, is in front of the operculum. In the figure the lateral articular 
denticles are shown rather too clearly, as in many instances they are scarcely perceptible. 
(5) Mucronella rostrigera, n. sp. (Pl. XIX. fig. 2). 
Character. — Zoarium rather thick, surrounding an Echinus- spine, white, and dull; the 
wall appearing to be formed of excessively fine, interlaced fibres. Zooecia ovate, distinct, 
moderately convex. Orifice subtrifoliate, the peristome being raised into a broad 
tooth on either side, and into a strong conical mucro in front which eventually becomes 
rostriform and supports a rounded avieularium on the summit. Ooecia subglobose, 
partially immersed ; surface entire with a faintly marked oval elevation on each side 
below. Operculum nearly circular, 0"‘004. 
Habitat . — Prince Edward Island, 80 to 150 fathoms. 
