_Mandibles_, with four teeth; the inferior angle blunt and broad, showing, apparently, a rudiment of a fifth tooth; the first tooth is as far from the second, as is this from the inferior angle; second, third, and fourth teeth very blunt, whole inferior part of mandible not much narrowed. Maxillæ small, with a small notch under the three upper spines, which are followed by five or six pair, nearly as large as the upper spines. _Cirri._--First pair remote from the second; their rami nearly equal, and about one third of the length of the rami of the second cirrus; thickly clothed with bristles: rami of the second cirrus of equal thickness, but little shorter than those of the sixth cirrus; the three or four basal segments of the anterior ramus are thickly clothed with spines; the other segments, and all the segments on the third pair, resemble the segments of the three posterior pair. These latter are elongated, not protuberant, and support eight pairs of spines with very minute intermediate spines; those in the dorsal tufts are numerous and long. _Caudal Appendages_ nearly as long as the pedicels of the sixth cirrus; oval, moderately pointed, with their sides, for one fourth of their length, thickly clothed with long very thin spines. _Affinities._--In the form of the scuta and of the carina this species is most nearly allied to _D. Grayii_ or _D. pellucida_, in the form of the terga to _D. Warwickii_. 5. DICHELASPIS ORTHOGONIA. Pl. II, fig. 10. _D. scutorum basali segmento angustiore quam occludens segmentum; longitudine ferè dimidiâ; duorum segmentorum junctione calcareâ: tergorum prominentiis marginalibus inæqualibus quinque: carinâ deorsum in parvo calyce lunato terminatâ._ Scuta with the basal segment narrower than the occludent segment, and about half as long as it; junction of the two segments calcified. Terga with five unequal marginal projections. Carina terminating downwards in a small crescent-formed cup. Maxillæ with the inferior part of edge much upraised. Hab. unknown; associated with _Scalpellum rutilum_, apparently attached to a horny coralline. British Museum. The specimens are in a bad condition, not one with all the valves in their proper positions, and most of them broken; animal’s body much decayed and fragile. _General Appearance._--Capitulum apparently much flattened; valves naked, coloured reddish, separated from each other by thin structureless membrane.