_Parietes_: the parietal tubes have not transverse septa; but are solidly filled up in their upper parts by dark-purple layers of shell. The _radii_, as already stated, are either not at all developed, or are extremely or only moderately narrow, with their summits more or less oblique: in Mr. Cuming's collection, however, there is an unique specimen, _var. mirabilis_ (Pl. 5, fig. 1 _c_) with the aperture of the shell as wide as the basis, with bright purple parietes, and white, very broad radii, having their summits parallel to the basis. The septa of the radii are finely denticulated, and the interspaces are filled up solidly. The _alæ_ have very oblique summits, and their edges are finely crenated. _Basis_, flat, or deeply cup-shaped; there is often an underlying, coarsely-cancellated layer. _Mouth_: labrum finely hairy, but without any teeth; mandibles, with the 4th tooth small; the 5th confluent, with the sometimes smooth, sometimes pectinated inferior angle. Maxillæ, rather broad, with a slight notch under the upper pair of spines. _Cirri_, first pair, with one ramus, having 29 segments, and above one third longer than the shorter ramus, having 17 segments; these latter segments are remarkable by the extent to which their upper front surfaces are laterally produced into projections, twice as long as the breadth of that portion of the segment which is articulated to the adjoining segment. These projections have a double row of serrated spines on their upper edge, and a beautiful radiating bundle at the end; the projections decrease in length, both in the upper and lower segments. The second cirrus (Pl. 29, fig. 4) has the segments (13 in number, in the same individual with the segments above enumerated) of both rami produced in the same singular manner as in the first pair. The third pair have only inverted conical segments, coloured darker purple than the other cirri. The sixth pair had in the same individual 31 or 32 segments, and therefore one or two more than in the longer ramus of the first pair.[93] The segments in the posterior cirri have their anterior faces shield-shaped, and bear 6 or 7 pairs of spines, with some minute intermediate spines. There is the usual point at the dorsal basis of the penis. [93] Under the Genus (p. 190) I have given the numbers of the segments in the cirri of this species at successive ages.