Pvn H,i I'UitlS

axinus. 247
This exhibits all the
of the London Clay as the type.
essential generic characters, except in respect of the
of the matrix
hinge, which is not visible in consequence
in which the shell is imbedded being too hard and com-
pact to be removed. It is remarkable, however, that
Sowerby added to his description of Axinus, " I suspect
it has no teeth."
Several names for this genus have been attributed to
Leach, viz. Thyasira, Thiatira, Thiatisa, and Bequania.
The first only is classically correct. Turton called it
Cryptodon, Philippi Ptychina, and I gave another generic
name (Clausina) to one of the species. All these are
mere synonyms and superfluous.
I would recommend those of my readers who are
acquainted with the Danish language to read a very
interesting account by Professor Sars of the animal of
A. Sarsii, contained in his Report of a zoological ex-
cursion to the Loffoden Isles and Fimnark in 1849.
He observes that Axinus differs from all other Con-
chifera in the position of its generative organs, which
lie outside the stomach, and not within it ;
and he com-
pares this genus to the Brachiopoda in that respect.
He found by a microscopical examination that some
individuals were male and others female.
1. Axinus flexuo'sus *, Montagu.
Tellina flexuosa, Mont. Test. Brit. p. 72. Lucina flexuosa, F. & H. ii.
p. 54,
xxxv. f. 4.
pi.
Body clear white : mantle somewhat contracted on the pos-
terior side, so as to form a round hole :
brown colour : foot placed in the middle of the ventral area.
gills thick, of a red-
Shell roundish-oval, tumid, thin, usually opaque but some-
times more or less transparent, scarcely glossy :
* Flexuous.
sculpture, irre-