_Penis_, short, blunt, thick at the apex, with one or two spines on it. I did not see any ovaria, but this could hardly have been expected in specimens in a dried condition, without they had happened to have been in a gorged condition. Certainly there were no ova. In the general summary at the end of the genus, I shall give my reasons for believing this parasite to be the Complemental Male of the _Scalpellum rostratum_. 5. SCALPELLUM PERONII. Pl. VI, fig. 6. SMILIUM PERONII. _J. E. Gray._ Annals of Philosoph., new series, tom. x, 1825. ---- ---- . . . . . Spicilegia Zoologica, tab. iii, fig. 10, 1830. ANATIFA OBLIQUA. _Quoy_ et _Gaimard_. Voyage de l’Astrolabe, Pl. xciii, fig. 16, 1823-1834. POLLICIPES OBLIQUA. _Lamarck._ An. sans Vertebres (2d edition). _S. (Herm.) valvis 13: laterum paribus tribus; pari superiore multùm elongato: pedunculi squamis calcareis nullis._ (Herm.) Capitulum with 13 valves: three pair of latera; upper latera much elongated: peduncle without calcareous scales. 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.