Pvn H,i I'UitlS

venus. 347
because of its tendency to vary. Although the general
shape and colouring are the same, an endless diversity
occurs. In young and half-grown specimens of the
variety laminosa the edges
of the ribs at the sides are
sharp and prickly, as in V. Casina. In adult examples
of the variety gibba the crenulations on the inside mar-
gin are apt
to become more or less obliterated. I have
one from Oban which is twisted and inequivalve.
Availing myself of the candid admission made by the
authors of the '
British Mollusca/ that " it is perhaps a
matter of controversy whether the Venus galli7ia of Lin-
naeus is specifically distinct from the one so designated
by the British writers/'' I have reunited with that spe-
cies the Pectunculus striatulus of Da Costa. The only
difference that I can detect between the shells from the
Mediterranean and our own coasts is, that the former
have usually (but not invariably) a purplish-brown stain
inside at the posterior extremity ; this I cannot regard
as a sufficient mark of distinction. The only other
points of comparison indicated by Forbes and Hanley
are common to both forms, as will appear from a critical
examination of the characters given in my description
of the species and several varieties. Linne named the
northern form in his l Fauna Suecica' V.gallina; and
in the tenth edition of his '
although, Systema Naturae/
he mentions the Mediterranean only, in the more com-
plete and universally recognized edition (the twelfth) he
first cites the '
Fauna Suecica '
and then says, ' c
Habitat
in M.Mediterraneo, Norvegico, Asiatico." His diagnosis
would include both the northern and southern forms.
Muller,
in his e
Zoologies Danicse Prodromus/ describes
the Scandinavian shell as V. gallina. I am aware that,
according to Deshayes, the siphonal tubes in specimens
which he examined on the Algerine coast are much