Having so lately described in the Memoirs of the Palæontographical Society, the fossil species, I will not here further allude to them, than to state, that out of the fifteen species therein described, _S. magnum_ comes very close to the recent _S. vulgare_, and that several Eocene and Cretaceous species, such as _S. quadratum_, _S. fossula_, and _S. maximum_, are allied to _S. rutilum_ and _S. ornatum_. _Scalpellum villosum_, a recent species, has stronger claims than any other species to be generically separated; and its habits, in not being attached to horny corallines, are also different, but the identity of its Complemental Male with that of _S. Peronii_, and its numerous points of resemblance in structure with the other species, have determined me not to separate it. _Scalpellum Peronii_, _villosum_, and _rostratum_, in having a sub-carina,--in the rostrum being pretty well developed,--and in the Complemental Male being pedunculated, and furnished with a functional mouth and prehensile cirri, may be separated from _S. vulgare_, _ornatum_ and _rutilum_; but even between these two little groups, _S. rostratum_ is in some respects intermediate, namely, in having three pairs of latera, and more especially in the rudimentary condition of the valves of its Complemental Male, and in the position in which the male is attached to the hermaphrodite. The three species in the second little group, namely, _S. vulgare_, _S. ornatum_, and _S. rutilum_, are more nearly allied to each other in all their characters, especially in the characters drawn from their Males, than are the other three species. _S. ornatum_ and _S. rutilum_ are considerably nearer to each other than any other two of the species. Upon the whole I conclude that the six species must be thrown either into five or into four genera (the first three species making one genus), or all into one genus, and this latter has appeared to me the preferable course. The separation even of Scalpellum and Pollicipes, as already stated, is hardly natural. The fact of these genera having existed from a remote epoch, and having given rise during successive periods to many species now extinct, is probably the cause that the few remaining species are so much more distinct from each other, than is common in the other genera of Lepadidæ. Whenever the structure of the whole capitulum in the fossil species is well known, and as soon as more species, recent and fossil, shall have been discovered, then probably the genus Scalpellum will have to be divided into several smaller genera.