Pvn H,i I'UitlS

ASTARTE. 317
It is not less variable than A. sulcata ; and if a spe-
form were
cimen of the smooth, flat and triangular
placed side by side with the fine-ribbed, convex and
rounded it variety globosa, would be difficult to imagine
that they were the same species. A. compressa, in all
its phases, may be known from any of the smooth- edged
varieties of A. sulcata by its inferior size, the shape
being always more triangular than square,
the beaks
being more central, and by the ribs (where they exist)
being much finer and more numerous in proportion to
the size of the shell. I received from Mr. Dawson of
Cruden a specimen found by him in the Moray Firth,
which had the hinge reversed, the right valve exhibiting
the teeth that properly belonged to the left valve, and
vice versa. The muscular impressions were as usual ;
but that would be the case, whether the right valve
had changed place with the left or they had retained
their normal relation to each other. I am not aware of
The
a similar instance of such a partial transposition.
instances of Lucina Childreni and Chama Lazarus, men-
tioned by Gray in the c
Zoological
Journal '
and '
Philo-
sophical Transactions/ are different, inasmuch as those
shells are inequivalve. Bivalve mollusca can never be
completely reversed like univalves, because the internal
and those of the
organs of the former are symmetrical,
latter are confined to one side or position.
I have before observed that this is not the Venus
compressa of Linne. Among the many synonyms of
our species may be mentioned V. Montacuti, Turton,
Nicania Banksii, Leach, Crassina convexiuscula and
C. obliqua, Brown, A. multicostata and A. Uddevallensis,
J. Smith, A. pulchella, Jonas, and A. propinqua, Lands-
borough.