Pvn H,i I'UitlS

218 kelliidjE.
leading
characteristics of each. With the former it
agrees in having the cartilage placed
at the shorter end
of the shell, a position contrary to that in Kellia, and
with the latter in the mantle being folded on the ante-
rior side, though not so completely as in that genus.
The position of the cartilage or ligament is by no means
unimportant, because it indicates the posterior side ;
and
the empty shell thus serves to determine the place, and
often the nature, of the organs which had composed the
frame of its late occupant.
It is very probable that the shell which Adanson
called " Le Poron " belongs to this genus ; but his
notice of it is unusually brief and obscure. He says that
it has two small triangular teeth in each valve, which
form the hinge, that it is at most only two lines in dia-
meter, and that it is whitish and sometimes of a violet
colour, chiefly towards the hinge. He evidently did not
know the animal, for he included the Poron among the
species of his genus Chama, which he described as having
three openings in the mantle, two of which take the form
of a rather long tube. It would be a waste of etymological
researchwere we to endeavour to trace the derivation
of the word " Poron." Adanson tells us, in the preface
to his most admirable work on the Mollusca of Senegal,
that he preferred inventing such chance names as had
the least meaning, and had no relation to other names
or known objects. Perhaps Dr. Leach had the same
idea in selecting some of his generic names. However
that may be, in his posthumous work on the Mollusca
of Great Britain he seems to have changed Lascea for
the more classically correct name of Autonoe, placing it
in the family Veneridce, although calling the species (after
" 33
describing it) Lasea rubra.
The Lascea are of a minute size, and usually inhabit