test, giving it a green appearance, Quoy and Gaimard's figure shows this green colour near the base of the specimen figured. The test is strong and substantial, of a leathery nature, and frequently more or less cartilaginous. It is often about ⅛in. in thickness. The blue colour extends almost through the thickness of the test.

The mantle is well developed; it is not attached firmly to the test except at the siphons, and is thick, opaque, and of a yellow colour. The muscles are not grounped into strong bands, but form a close network of small bundles. Some larger bands can be seen on the inner side of the mantle.

The branchial sac (fig. 1) has four well-marked folds on each side; the two ventral folds are smaller than the others. About 10 internal longititudinal bars occur on a fold, and usually 3, sometimes 4, in the interspace; the bars are wide and ribbon-like. The following table, compiled from the examination of seven typical specimens, shows the variation of the number of these bars on the folds of each side; the folds are numbered from dorsal to ventral.

Fig. 1.—Part of the branchial sac of Styela coerulea, from an interspace; × 25.

The internal longtitudinal bars are much closer on the folds than in the interspace, and the meshes are square on the folds, but oblong transversely in the interspace. The transverse vessels sometimes branch and make parts of the sac appear rather irregular. These vessels also very considerably in width; in some cases they are as wide as the meshes, and vary from this extreme to slender vessels, which may, though very rarely, imperfectly divide two meshes. Sometimes many wide vessels are present, but usually several narrower ones appear between the widest (fig. 1). The number of stigmata in a mesh also varies greatly, 6 up to 12 or 15 being commonly found. On the folds there are 4 to 6 in a mesh. The stigmata are wide and clearly defined, and are lined by cilia.

The endostyle is prominent; the groove itself is narrow, and anteriorly joins the well-marked perioesophageal ring.

The dorsal lamina is a plain broad membrane, slightly puckered, and generally is found bent upwards to the right, forming a groove. In one specimen examined this groove contained a strand of what was apparently food material in the act of passing from the lamina into the oesophagus.

Fig. 2.—Part of the ring of tentacles of Styela coerulea, × 13. t, t′, t″, long, medium. and short tentacles respectively.

Fig. 3.—Dorsal tubercle of Styela coerulea; × 25. d, dorsal lamina; p, perioesophageal tract; s, slit.

The tentacles (fig. 2) are simple, and, on an average, number 80. Roughly, three sizes may be recognized: (a.) The largest extend almost to the centre of the siphon; of these there are about 20. (b.) The medium-sized tentacles also number about 20, and alternate with the largest. (c.) The smallest tentacles, each of which lies between an (a) and a (b), number about 40.

The dorsal tubercle (fig. 3) is circular in outline, except for a slight indentation on the anterior surface. The slit is S-shaped, the left limb having a wider curve than the right. I have found this structure fairly constant; very few of the specimens examined showed a different form of slit.

The alimentary canal (fig. 4) is situated in the posterior half of the body, and is attached to the left side. It forms a narrow loop, the bend of which

reaches, forwards very little past the atrial siphon. The junction between the oesophagus and stomach is well marked, but the stomach tapers gradually into the intestine and rectum. There is no digestive gland. On the surface of the stomach several large blood-vessels can be seen; internally the stomach has very prominent longitudinal folds.

Fig. 4.—Alimentary canal and gonads of Styela coerulea; × nearly 2. The right side of the body and the branchial sac have been removed. a, anus; at,-atrial siphon; br, branchial siphon; g, gonads of left side; m, mantle; oe oesophagus; r, rectum; s, stomach; t, ring of tentacles.

The gonads consist of two masses of short, thick, irregular, tube-like structures, which are attached to the mantle, one mass on each side (fig. 4). Sometimes these organs branch, and there are usually 6 to 9 or more of them on each side. They are usually placed near the bend of the intestinal loop, but may extend from the tentacles to the posterior end. The gonads and the alimentary canal are closely associated with numerous pouch-like structures, which have been described under the name of “endocarps” and are common to several genera of the Cynthiidae

Habitat.—Rocky shores of Hauraki Gulf; Great Barrier Island; Bay of Islands (Oliver). Common under rocks at low water.

This species cannot be mistaken, as its beautiful colour makes it a very conspicuous object. On the rocky shores of Hauraki Gulf it is the common Ascidian; it is also very common, at Great Barrier Island. Mr. W. R. B. Oliver informs me that this species is also very plentiful at the Bay of Islands, where he collected some specimens, and I have to acknowledge my indebtedness to him for placing these at my disposal.

Apparently this Ascidian was collected in 1835 by Quoy and Gaimard, of the “Astrolabe,” who described and figured it under the name Ascidia coerulea; but internal structure—viz., the 4 folds of the branchial sac on each, side, the condition of the alimentary canal, and the gonads—shows it to belong to the genus Styela. The figure illustrating their account of the species exaggerates the 4-lobed structure of the branchial opening: When partly closed both siphons are decidedly 4-lobed, but not to the extent figured. Quoy and Gaimard also describe a double violet line in the siphons, but none of my specimens shows this, nor does their figure show it.

I have collected several other species in the gulf which do show violet lines in the siphons, but externally they are quite different, and have no