iella, and Xiphidium.
Scalpellum blends through _S. villosum_ into Pollicipes; and this latter
genus has an equal right with Scalpellum, to be divided into sub-genera,
three in number. Hence, no less than eight genera might be made out of
the twelve recent species of Scalpellum and Pollicipes, and their
formation, in some degree, be justified; but, in my opinion, this
inordinate multiplication of genera destroys the main advantages of
classification. At one time, I even thought that it would be best to
follow Lamarck, and keep the twelve recent species in one genus; but
considering the number of fossil species, I believe the more prudent
course has been followed, in retaining the two genera Scalpellum and
Pollicipes; more especially as I can hardly doubt, that several other
species will be hereafter discovered.

Having so lately described in the Memoirs of the Palaeontographical
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.