278 
THE VOYAGE OF H.M.S. CHALLENGEE. 
Supplementary Account of Species of Microsclerophoea not in the Challenger 
Collection. 
Family I. Placinida:, F. K Sclmlze. 
Microsclerophora with tetractinose, triaetinose, and diactinose asters, and sometimes 
mono-, di-, or tri-lophose candelabra. The canal-system is either eurypylous or aphodal ; 
the mesoderm chiefly collenchymatous. The sponge is divided into a hypomere and 
spongomere. 
Genus 1. Placina, F. E. Schulze. 
Sponge. — Thin, flat, incrusting the under sides of stones or other foreign bodies. 
From the free surface one or more oscular tubes project. Canal-system eurypylous, 
mesoderm scanty, entirely collenchymatous. The spicules are tetractinose, triactinose, 
and diactinose asters and candelabra. 
Placina monolopha, F. E. Schulze. 
Plakina monolopha, F. E. Schulze, Zeitschr. f. wiss. Zool., Bd. xxxiv. pp. 407, 448, pi. xx. 
figs. 1-7 ; pi. xxii. figs. 22-29, 1880. 
Sponge. — Thin, flat, incrusting, margin irregularly rounded, or lobate, lobes some- 
times anastomosing ; raised into a smooth wall by a continuation upwards of the hypo- 
mere, one or more oscular tubes proceed from the margin. Surface minutely mammillated. 
Pores split-like openings in the intervals between the mammillae, Hypomere simple. 
All the pinnacocytes bear flagella. Hermaphrodite. 
Spicules. — 1. Asters, tetractinose {microcaltlirops), triactinose (microtriods), and 
diactinose {microxea); actines straight or curved, of the asters 0‘025 to 0’03 mm. long, 
of the microxeas, from 0'035 to 0'045 mm. in total length. 2. Candelabra, monolophose, 
the three simple actines usually curved, simply or sigmately. 
Colour. — Pure white, or faint rose colour ; size, small, 1 to 3 mm. in thickness. 
Habitat. — Trieste, Lesina and Naples ; from 1 to 2 fathoms. 
Placina dilopha, F. E. Schulze. 
Plakina dilopha, F. E. Schulze, Zeitschr. f. wiss. Zool., Bd. xxxiv. pp. 422, 448, pi. xx. 
figs. 8-11, 18; pi. xxii. fig. 30, 1880. 
Sponge. — Irregular, round, incrusting plates, without a marginal wall. Oscular tube 
not marginal. Pores simple round openings of different sizes, Hj^pomere simple ; 
ectosome thin. 
