_Maxillæ_ with three large upper unequal spines, beneath which, there is a deep and wide notch (bearing one spine), and the inferior part projects highly, bearing three or four pairs of spines, and is, itself, obscurely divided into two steps. _Outer Maxillæ_, very sparingly covered with bristles; outline, hemispherical. _Cirri._--The rami of the five posterior pair are extremely long, as are the pedicels; the segments are much elongated, with their anterior faces not at all protuberant; each bears five pair of very long and thin spines, with an excessively minute one between each pair; the dorsal tuft consists of very fine and thin spines. The second cirrus has its anterior ramus not at all thicker than the posterior ramus; but has an exterior third longitudinal row of small bristles. First cirrus, separated by a wide interval from the second pair; very short with the two rami slightly unequal in length; the segments are broad, and are paved moderately thickly with spines; the terminal spines not particularly thick. _Caudal Appendages_ consist of very small and narrow plates, about half the length of the pedicels of the sixth cirrus, with a few long spines at their ends. This well-marked species, I think, has not more affinity to one than to another of the previous species: it differs from all, in the junction between the two segments of the scuta being perfectly calcified; in the peculiar cup, forming the base of the carina; and lastly, in the inferior part of the maxillæ projecting. OXYNASPIS.[33] _Gen. Nov._ Pl. III. _Valvæ 5, approximatæ: scutorum umbones in medio marginis occludentis positi: carina rectangulè flexa, sursùm inter terga extensa, termino basali simpliciter concavo._ Valves 5, approximate; scuta with their umbones in the middle of the occludent margin; carina rectangularly bent, extending up between the terga, with the basal end simply concave. [33] From [Greek: oxunô], to sharpen, and [Greek: aspis], a shield or scutum. Mandibles with four teeth; maxillæ notched, with the lower part of edge nearly straight, prominent; anterior ramus of the second cirrus thicker than the posterior ramus; caudal appendages, uniarticulate, spinose. Attached to horny corallines.