Pvn H,i I'UitlS

310 CYPRINIDJE.
crenulation of the inside edge was a sign of maturity,
although some conchologists suggested that it might
denote a sexual difference ; but the former is opposed to
my own observation (especially as regards A. triangularis),
and no investigation appears to have been made
to warrant the latter. Dr. Malm has offered another
explanation, by showing that when the margins
in the
course of growth meet on a rib the inside is notched,
but if they meet on a furrow it is plain ; and he observes
that the same takes place in species of Murex, which
have the inside of the outer lip grooved in perfect ex-
amples. To that extent, therefore, the character is
correlative with development : but it is exhibited by
A. triangularis, which never has any ribs;
I have adult
specimens of A. sulcata with the margin quite plain and
smooth in front, but distinctly notched on each side ;
and A. compress a has always a plain edge, although the
shell is ribbed. Some of the cardinal teeth are often
rudimentary or so indistinct that, without a close scru-
tiny, there appear to be only two teeth in the right, and
one in the left valve, which locks into a hollow space
between the opposite pair.
Astarte may be said to be " at home " in the far north.
Only two species inhabit the Mediterranean, and those
while thrice that number abound within the
sparingly,
Arctic circle. They frequent sand, more or less mixed
with mud, at various depths ; but none are littoral. Many
species of remarkable productiveness swarmed in tertiary
seas. Fossil shells of that group of Venus which is
represented by V. fasciata may easily
be mistaken for
species of Astarte, some of the characters which distinguish
the latter genus being lost by the removal of the
colour and epidermis.