SCALPELLUM. 15 
here repeat the remarks made in the Introduction on the great difficulties in classifying the 
recent species, and still more the fossil species of Scalpellum. I may, however, here state 
that should the S. vw/gare be hereafter kept distinct in a genus to itself, 8. magnum would 
have to go with it. Should a recent species, which in a future work I shall describe under 
the name of S. rutilum, be generically separated, it will probably have to bear the name of 
Xiphidium, from its alliance to the Eocene X. guadratum of Sowerby, to which species the 
cretaceous S. fossula and several other forms are apparently closely allied. These fatter 
species, however, are likewise closely allied to the Scalpellum ornatum, which Mr. Gray has 
already raised to the rank of a genus under the name of Thaliella. ‘There are some 
fossil species, as S. arcuatum, and simplex and solidulum, which I cannot rank particularly 
near any recent forms. Mr. Sowerby founded the genus Xiphidium on the umbo in the 
Carina being situated at the apex, and on its growth being consequently exclusively 
downwards. ‘This is likewise the case with the recent S. rutilum ; but I shall have 
occasion to show, under S. magnum, that the upward growth of the Carina in that 
and other species of the genus, depends merely on the intra-parietes, which are present in 
many species, meeting each other and being thus produced upwards. Moreover, in the 
recent S. ornatum, the position of the umbo is variable, according to the age of the 
specimen ; in half-grown individuals beg seated at the apex, and in large specimens 
being sub-central, as in S. vulgare, magnum, and other species. I should have been very 
glad to have retained the genus Xiphidium, but taking into consideration the whole 
organisation of the six recent species, I can only repeat that we must either make six 
genera of them, or leave them altogether, and this latter has appeared to me the most 
advisable course. 
Sexual Peculiarities.—For reasons stated in the Introduction, I have kept the genera 
Scalpellum and Pollicipes distinct ; but I may mention, in order to call attention to a point 
of structure which may hereafter be discovered in some fossil species, that [ was much influ- 
enced in this decision by some truly extraordinary sexual peculiarities in all six recent species 
of Scalpellum. Scalpellum ornatum is bisexual ; the individual forming the ordinary shell, 
is female ; each female has two males (a case of Diandria monogynia), which are lodged in small 
transverse depressions, one on each side, hollowed out, on the inner sides of the Scuta, close 
above the slight depressions for the adductor scutorum muscle ; in &. rutilum 
(nov. spec.) two males are lodged in the same place on each side, but 
rather in concavities in the valve, than in distinct depressions. As these are . 
the two recent species most nearly related to several Cretaceous and Eocene 
forms, we might expect to find similar depressions in some fossil species ; but 
as yet I have not succeeded in distinctly finding such. 'The male cirripedes 
are very singular bodies ; they are minute, of the same size as the full- = 
grown larva; they are sack-formed, with four bead-like rudimental valves at Inside view of theScutum 
in Scalpellum ornatum. 

(A) is the depression for 
their upper ends; they have a conspicuous internal eye ; they are absolutely fhe aductor husete 
destitute of a mouth, or stomach, or anus: the cirri are rudimental and furnished 
