Mandibles with 10 or 11 unequal teeth: maxillæ with the edge nearly straight, bearing numerous spines.

Complemental Male, attached externally, between the scuta and below the adductor muscle; pedunculated; capitulum formed of six valves, with the carina descending far beneath the basal angle of the terga; mouth and cirri prehensile.

Swan River, Australia, attached to a coralline; Mus. Cuming. Port Western, Bass’s Straits, as stated in the Voyage of the Astrolabe. Mus. Brit.

HERMAPHRODITE.

Capitulum formed of 13 valves; namely, two scuta, two terga, a carina and sub-carina, a rostrum, a pair of upper latera, and two pair of lower latera; these latter valves, with the sub-carina and the rostrum, make a whorl of six pieces. The upper part of the capitulum is, as usual, produced. The upper valves are separated (in specimens which have not been dried) by rather wide interspaces of membrane; they are covered (excepting, generally, their umbones,) by membrane, which in the interspaces is clothed with fine spines. The spines, or the marks where they were once articulated, are visible over nearly the entire surface of the membrane covering the valves. The spines are particularly numerous round the orifice of the sack. The whole capitulum, (in a dried condition), is coloured dull purplish-red, which is only in part due to the underlying corium, for the valves themselves are pale red. After having been long kept in spirits, the whole capitulum becomes colourless. The valves are smooth, faintly marked by lines of growth. The umbones of the lower valves project outwards, giving a denticulated appearance to the base of the capitulum.

Scuta, slightly convex, oblong, breadth about two thirds of the length, almost quadrilateral, with the upper portion produced into a flat projection; this projection is almost spear-shaped, being constricted a little on each side below the apex. There is a deep pit for the adductor muscle. The umbo is near the apex, the part above not being above one fifth of the whole length of the valve. As in S. vulgare, the growth is at first downwards, and subsequently a little upwards and downwards, thus producing the upper, small, spear-like projection, which lies at a lower level than the umbo. There is a fold on the occludent margin.

Terga, large, flat, triangular; carinal margin slightly hollowed out; occludent margin slightly arched, with a small portion protuberant to a variable amount. The apex is slightly curved towards the carina.

Carina, long, internally deeply concave, angularly bent, the lower portion slightly longer and wider than the upper part; the two halves meet each other at about an angle of 135°; the upper half is parallel to the longer axis of the terga, between which it extends for three fourths of their length. The external surface is rounded, except near the umbo, where the edge is carinated; growth almost equally upwards and downwards; the parietes and tectum are not separated by ridges.

The Sub-carina lies close under the carina, and is placed almost transversely to the longer axis of the capitulum; external surface arched and smooth, the whole having the shape of half of a cone, with the apex a little curved outwards; seen internally, it may be said to be formed of two triangular wings placed at right angles to each other; basal margin straight; in size equalling the carinal latera.

Rostrum, lying almost transversely to the longer axis of the capitulum, under the basal margins of the scuta; in shape ([fig. 6 a]) closely resembling the sub-carina, but about one third larger than it; larger also than either the rostral or carinal latera; seen externally, appears like a half cone; seen internally, is formed of two triangular wings (with curved edges), placed at right-angles to each other.