Pvn H,i I'UitlS

GASTRANA. 367
tricose shell, as well as in the greater size of the anterior
cardinal tooth in the left valve, and the want of lateral
teeth. But all these characters exist in species of the
parent or typical genus. The shell of T. balaustina is
nearly equally convex; T. squalida and other species have
the anterior cardinal tooth in the left valve as large in
proportion to the other tooth ; and T. balthica has no
lateral tooth. However, as I have before remarked, there
are no lines of absolute demarcation between any two
allied genera and there ; may be as good reason for separating
Gastrana from Tellina, as Tapes from Venus.
in 1845 the name of Diodonta for
Deshayes proposed
this genus, being (it may be presumed) unaware of
Schumacher's publication, which bears the date of 1817.
The one selected a European, and the other tropical
types ;
but all are congeneric.
Gastrana fra'gilis *, Linne.
Tellina frag His, Linn. Syst. Nat. p. 1117. Diodonta fragilis, F. & H. i.
p. 284, pi. xxi. f. 3, and (animal) pi. K. f. 2.
Body yellowish- white : tubes almost twice as long as the
shell is broad, one having eight and the other six rays or
points at their orifices ; alimentary
tnbe sheathed at its base
foot rather large (Deshayes).
Shell triangular, considerably produced at the posterior
end, more convex towards the beaks, rather thin but opaque,
somewhat glossy when young but afterwards becoming lustre-
less : sculpture, more or less irregular, thin, concentric ridges
or laniinse, which are slightly imbricated on the posterior side,
besides numerous minute and close-set parallel strise in the
interstices of the ridges ; the whole surface is also covered
with fine longitudinal striae which radiate from the beaks, and
are three times as many as the transverse ridges, but very
much more slight and scarcely raised where these cross the
;
ridges the crests of the latter are indistinctly beaded: colour
* Brittle.