radiate from a centre.

17. Flustra, Linn.

a. Cells on one side only.

1. F. pyriformis ?, Lamouroux.

Cells pyriform, or barrel-shaped, prominent, marked with transverse
wrinkles. Ovicells lofty, keeled in front, with a strong central, and two
lateral longitudinal ribs.

Habitat: Bass Strait, 45 fathoms.

Sometimes small and parasitic, upon Sertularians and Polyzoa--sometimes
independent, then of large growth, forming dichotomously divided fronds,
with strap-shaped truncate, unequal divisions.

b. Cells on both sides. (Carbasea, Gray.)

2. F. denticulata, n. sp.

Cells much elongated, narrow; sides parallel, ends square; an upturned
spine on each side at the oral end; sides of cell denticulate, denticles
very numerous, small, acute. Avicularia irregularly distributed on the
surface of the frond.

Habitat: Bass Strait, 45 fathoms.

Frond divided into numerous strap-shaped, truncated segments, of various
widths; it attains a height of several inches. In habit it is very like
some forms of F. truncata, and there is a Mediterranean species
(undescribed ?) in which the cells are denticulate, much in the same way
as in the present species, but otherwise quite distinct.

18. RETEPORA, Lamarck.

Character. (B.) Polyzoarium foliaceous, calcareous, or horny, reticulate;
cells only on one side.

1. R. cornea, n. sp.

R. ambigua ? Lamarck.

Cells oval, not very regularly arranged, in a continuous, foliaceous,
subcircular frond; reticulated with oval spaces, not as wide as the
interspaces. Ovicells large, galeriform, immersed, smooth.

Habitat. Off Cumberland Islands, 27 fathoms, fine grey mud.

This remarkable species is so completely a Retepore in construction, that
it seems impossible to separate it from that genus, merely from the
circumstance that its composition is more horny than calcareous. The
frond is more or less orbicular, or rather is composed of more or less
orbicular or reniform folds, one over another, and attached as it were to
a common centre. The substance is very thin and transparent, and the
interspaces are much broader than the elliptical spaces.

2. R. cellulosa.

Habitat: Bass Strait, 45 fathoms.

Not distinguishable from a Mediterranean specimen.

3. R. ctenostoma, n. sp.

Frond umbilicate, irregularly infundibuliform, spaces elongated, narrow,
margins subdenticulate; interspaces as wide as the spaces. Mouth of cells
tubular, projecting; with six or seven unequal acute expand