2. R. cellulosa.

Habitat: Ba.s.s Strait, 45 fathoms.

Not distinguishable from a Mediterranean specimen.

3. R. ctenostoma, n. sp.

Frond umbilicate, irregularly infundibuliform, s.p.a.ces elongated, narrow, margins subdenticulate; inters.p.a.ces as wide as the s.p.a.ces. Mouth of cells tubular, projecting; with six or seven unequal acute expanding teeth.

Habitat: Ba.s.s Strait, 45 fathoms.

A very distinct and beautiful species. The frond is about half an inch wide, and though really umbilicate and subinfundibuliform, does not at first sight appear so, being much more expanded on one side of the centre than on the other.

19. ESCHARA, Ray.

1. E. lichenoides, M. Edwards. Mem. sur les Eschares. Ann. d. S. N. tome 6 page 31 plate 2 figure 3.

Habitat: Australian Sea, probably Ba.s.s Strait. (It also occurs in Algoa Bay.)

20. DIACHORIS, n. gen. Table 1 figures 10 to 12.

Cells separate, each connected with six others by short tubes; disposed in a horizontal plane, and forming a continuous irregular frond; free, or partially adnate.

The mode of arrangement and interconnection of the cells in this genus is remarkable, and highly interesting. It represents, in fact, a dissected Fl.u.s.tra or Membranipora. The cells are disposed in linear parallel series, and those of two contiguous series are alternate with respect to each other. Each cell is connected with one at either end in the same linear series by a rather wide short tubular prolongation, and with two on each side in the contiguous series by narrower tubes, so that each cell, except in the marginal rows, is connected with six others. It is this mode of interconnection of the cells that affords the diagnostic generic character. There is but one species in the present collection, but in Mr. Darwin's there are two others from the Straits of Magellan, as yet undescribed.

1. D. crotali, n. sp. Table 1 figures 10 to 12.

Cells erect, open in front, perforated on the sides and bottom; a lanceolate appendage articulated to each upper angle. Ovicell conical, placed on the upper edge.

Habitat: Ba.s.s Strait, 45 fathoms.

The frond, though not strictly speaking adnate, as it seems to have no attachments, is usually spread loosely over other polyzoa. There is no appearance of a movable mandible in the lanceolate appendages, but which, nevertheless, most probably represent avicularia. These organs are of a lanceolate form, with an elevated ridge or keel along the back, and slightly concave beneath. They project in front, slightly depending; and at the base of each is a rounded eminence.

Fam. 6. CELLEPORIDAE.

Polyzoarium missive or crustaceous, composed of ovate cells in juxtaposition and arranged, more or less regularly, in linear series, radiating from a central point or line.

21. CELLEPORA, Otho Fabricius.

1. Cellepora bil.a.b.i.ata, n. sp. ?

C. l.a.b.i.ata, Lamouroux.

Cells deeply immersed; mouths in some entire and unarmed; in others, with two ac.u.minated conical lips; immediately beneath the apex of the posterior lip a small sessile avicularium. Ovicells subglobular, with a scutiform area on the upper surface, marked with several lines on each side, radiating from a central line.

Habitat: Ba.s.s Strait.

Parasitic on several zoophytes. This species to the naked eye exactly resembles C. pumicosa, but on closer examination several important differences will be observable. The cells in C. bil.a.b.i.ata are less rounded and less distinct than in C. pumicosa. As in that species, some of the cells are furnished with an avicularium, and others unprovided with that appendage; and again, some cells support an ovicell, whilst others do not. The mouth of the unarmed cells in both species is more or less circular and plain, but in C. bil.a.b.i.ata, even in the unarmed cells, the mouth is occasionally distinctly bil.a.b.i.ate. In C. pumicosa the avicularium is placed subapically on a solitary posterior obtuse mucro, but in C. bil.a.b.i.ata there are two such processes longer and more pointed, one in front and the other behind the mouth; the avicularium, as in the former case, being placed immediately below the apex of the posterior mucro. The ovicells also differ very much. In C. pumicosa this organ presents several rather large circular spots or perforations ? whilst in C. bil.a.b.i.ata it exhibits a scutiform or horseshoe-shaped area, marked with several transverse lines on each side of a middle longitudinal line.

Fam. 7. GEMELLARIADAE.

Cells opposite, in pairs.

22. DIDYMIA, n. gen. Table 1 figure 6.

Cells joined side by side; opening large, oval; mouth subapical, central.

No avicularium. Ovicells contained within a cell, which is central at each bifurcation.

1. Didymia simplex, n. sp. Table 1 figure 6.

Cells oblong, narrowed below, broad and truncate, with an angle externally above. Back marked with transverse rugae.

Habitat: Ba.s.s Strait, 45 fathoms.

A fine species, growing in loosely-branched phytoid fronds, to a height of several inches. In some (dried) specimens the branches are a little incurved, but not in all. The situation of the ovicell is peculiar. It is contained within the upper part of a cell placed between, or rather in front of the pair, from which the two branches at a bifurcation take their origin. The ovigerous cell differs widely in form from the others, being pyriform, and much attenuated below; and the orifice is below the middle. The upper compartment, in which the ovicell or sac itself is lodged, appears to be separated from the lower by a transverse diaphragm.

23. DIMETOPIA, n. gen. Table 1 figures 7 to 9.

Cells joined back to back; the mouths of each alternate pair looking in the same direction, and at rightangles to the intermediate pair.

1. D. spicata, n. sp. Table 1 figure 9.

Cells infundibuliform. Margin of opening much thickened, with six equidistant, elongated pointed spines.

Habitat: Ba.s.s Strait, 45 fathoms.

White, transparent, forming thick tufts about 1 1/2 to 2 inches in height. The same species also occurs in New Zealand.

2. D. cornuta, n. sp. Table 1 figures 7 and 8.

Cells suddenly contracted about the middle. Opening oval, wide above; margins slightly thickened with a short thick conical horn on each side above, and a long projecting spine (rarely two) in front below.

Habitat: Ba.s.s Strait, 45 fathoms.

Branches narrower than in the preceding species. Colour yellowish. Tufts loose; ovicell small in proportion to the size of the cells. It is placed immediately above and behind the upper margin of the opening of the cell to which it belongs.

Suborder 3. CTENOSTOMATA.

Fam. 1. VESICULARIADAE. Cells tubular, h.o.r.n.y.

24. AMATHIA, Lamouroux.

1. A. biseriata, Krauss. Corall. der Sudsee, page 23. Figure 1 a, b, c.

Habitat: Swan Island, Banks Strait.

The biserial arrangement of the cells is not a sufficient character, because in Amathia cornuta (Lamouroux) the cells are also biserial as well as in another South African species, very like the Australian form probably intended by Krauss, but apparently different from it. In the South African form the cells are shorter, narrower, and more cylindrical, and the branches are terminated by two lanceolate tags, which are not present in the Australian species, in which latter the cells also are wider, longer, and prismatic, or subhexagonal, with very thin walls.