_Outer Maxillæ_, large and triangular. The inner margin is slightly concave, and continuously covered with short spines. The outer margin is bilobed, as in _S. vulgare_, with the basal part supporting a great tuft of long bristles, of which the greater number turn outwards, and almost cover the olfactory orifices. The latter are slightly prominent, placed some way apart from each other, with the above-mentioned tufts of bristles between them. All the spines of the trophi are in some degree doubly serrated. _Cirri._--The first pair is seated rather far from the second pair, and the prosoma being little developed, the shape of the body nearly resembles that of _S. vulgare_. The posterior cirri are elongated, very little curled, with the segments much flattened, not at all protuberant, bearing from five to seven pair of long serrated spines, with a few small spines in an exterior row; between each pair there is a very minute tuft of small bristles; the upper lateral rim of each segment is toothed with small spines; spines of the dorsal tufts, long, serrated. _First pair_, elongated, having numerous segments, namely, seventeen, whilst the sixth pair in the same individual had only twenty-one segments; rami nearly equal; segments short, nearly cylindrical, thickly clothed with long serrated spines. The _second_ and _third_ pair are nearly equal in length; they have their anterior rami slightly thicker than their posterior rami, both being much more thickly clothed with spines, than are the three posterior pair of cirri. Pedicels, rather short, with their inner edges not forming a projection, as in _S. vulgare_. _Caudal Appendages_ (Pl. X, fig. 20), uni-articulate, flat, rounded at their ends and moderately long; clothed most thickly, like brushes, with very fine bristles, which latter are serrated, and are longer than the appendages themselves. _Penis_, of small size, narrow, pointed, and thickly clothed with delicate hairs; in length equalling only one fourth of the sixth cirrus. _Ovigerous Fræna_, small, semicircular; entire edge thickly covered with glands. Ovarian tubes, within the peduncle, fully developed as usual. _Affinities._--This species differs from all the others in the absence of calcareous scales on the peduncle; but it has no other character which at all justifies its generic separation. In the shape of the scuta and carina it comes nearest to _S. vulgare_. Taking all the characters together, it is scarcely possible to say to which of the other species it is most closely allied, having close affinities with all. In the entire structure, however, of the Complemental Male, immediately to be described, this species certainly comes nearer to _S. villosum_ than to any other species. I may add, that in _S. villosum_ the latera are almost rudimentary, and therefore tend to disappear, whereas in _S. Peronii_ it is the calcareous scales on the peduncle which have actually disappeared. COMPLEMENTAL MALE. Pl. VI, fig. 3.