Pvn H,i I'UitlS

36 AXOMIIDJE.
ture, the number and position of its muscular scars, and
fiat (instead of raised) plug. It is also not so susceptible
of outward impressions as that species. An A. patelliformis
attached to a scallop, although it sometimes partakes
of its companion's ribs, has also its own natural
ribs, which run their independent course from the beak
to the margins. The orifice in young specimens is
nearly round. The prominent
beak somewhat resem-
bles the apex of a limpet. The plug lies in a hollow,
which is apparently made in the same way as I have
suggested with regard to the other species. Owing probably
to the green colour of the liver, the rostral area
or nucleus of the shell always appears to have a similar
tinge.
It is not without considerable hesitation that I have
ventured to unite with this species the A. striata of
Loven ; but, after examining his types at Stockholm,
and a long and careful comparison of a great many
specimens of this beautiful variety,
I cannot make out
any definite specific character. The only difference
consists in the more delicate sculpture of LoveVs shell;
and specimens may be observed in which the ribs and
striae blend so insensibly into each other, that it is im-
possible to say whether they belong to the typical spe-
cies or the variety. Judging from Linnets description
of A. patelliformis, this variety appears to correspond
with it better than the typical form. I consider it ana-
logous to the variety " aculeata " of the last species.
A. patelliformis has not received so many names as
A. ephippium, and I can only find fourteen of them.
The Ostreum striatum of Da Costa (but not that of
Lister) appears to be this species. It has been placed
by some conchologists in the genus Placunanomia of
Broderip ; but the distinctive character of that genus