_Generative System._ The ova are nearly spherical, and remarkably large, as was stated to be the case in the introductory discussion, in which the larva of _S. vulgare_, in the first stage of development, was described: the ovigerous fræna are small. The testes are large, but the vesiculæ seminales in some of the species extraordinarily small. _Scalpellum ornatum_, and perhaps _S. rutilum_, are unisexual; the other species are hermaphrodite, but most or at least some of the individuals, are furnished with Complemental Males. These latter are fully described under each species, so I will here only remark, that _S. ornatum_, which alone (excepting perhaps _S. rutilum_) is unisexual, has less claim than the other species to be generically separated: we have seen also, in Ibla, that similar sexual differences occur in two most closely allied species. It is very singular how much more some of the Males and Complemental Males in Scalpellum differ from each other, than do the female and hermaphrodite forms; this seems due to the different stages of embryonic development at which the males have been arrested. In the males, however, of _S. rostratum_, _S. Peronii_, and _S. villosum_, compared one with another, but not with the males of the other species, the parts of the mouth and apparently the cirri, resemble each other more closely, than do the same organs in the hermaphrodites. At the end of this genus I shall give a summary on the highly remarkable sexual relations both in Scalpellum and Ibla. _Distribution._--The species seem distributed over the whole world, but as far as we can trust our present scanty materials, are most common in the warmer temperate regions. The _S. vulgare_ ranges from the Norwegian seas to Naples. Most of the species are inhabitants of deep water. _Affinities._--In the preliminary remarks, we have seen how this genus blends into Pollicipes; and under the head of Oxynaspis, I have shown its close affinity to that genus. If, indeed, we take _Pollicipes spinosus_, and destroy all but six of the already minute and almost rudimentary latera, we shall, as far as the capitulum is concerned, convert it into a Scalpellum, closely similar to _S. villosum_. If we take any species of Scalpellum, (excepting _S. villosum_ and _S. rutilum_,) and destroy all the valves, but the scuta, terga and carina, we shall convert it into an Oxynaspis. Lastly, I have shown under Ibla, that in several most remarkable peculiarities of structure, there is a manifest affinity between Scalpellum and that genus. _Geological History._--Full details on this subject have been given in the Memoirs of the Palæontographical Society. I will here only state, that the oldest known form of Scalpellum occurs in the Lower Green Sand. [=T= SUB-CARINÂ NULLÂ.] 1. SCALPELLUM VULGARE. Pl. V, fig. 15. SCALPELLUM VULGARE. _Leach._ Encyclop. Brit. Suppl., vol. iii, 1824. LEPAS SCALPELLUM. _Linn._ Systema Naturæ, 1767.