Pvn H,i I'UitlS

20 TEREBRATULID.E.
mostly blunt and often worn by attrition, never much produced
: foramen triangular, occupying nearly the whole of the
dorsal area : deltidium :
exceedingly slight hinge-plate thick
and broad: teeth strong and : triangular sockets broad but not
deep : skeleton consisting of two very slight and narrow ribandlike
plates or ribs, placed as in A. decollata, but having only
their front edges free, the remaining portion being united with
the shell; within the upper valve is a septum, extending from
the centre of the hinge to nearly the front margin, besides a
few parallel but indistinct striae ;
the lower valve has a strong
blunt central ridge, which is higher in front and occupies about
half of the interior ; the front margin is minutely crenulated
inside. L. 0-06. B. 0-075.
Habitat :
East Shetland, Skye, and co. Antrim ;
Moray Firth (Dawson) ; Dublin Bay (Waller) ; Exniouth
(Barlee and Clark) ; Guernsey (Lnkis & J. G. J.). Fos-
sil in the Coralline Crag. Sars has found it at Chris-
tiansund, Bergen, and Manger in Norway ;
it on the Normandy coast ; and among
I have taken
some small shells
which I received through M. Verany from Sardinia was
a single valve of this species.
The animal closely resembles that of A. decollata.
The anterior occlusor or retractor muscles are of enormous
size, and their impressions on old shells are very
conspicuous and deep, somewhat resembling those of
Crania. Very young shells have scarcely any of the
tubular perforations ; and their beaks remind one of
the bill of a Platypus. These delicate processes become
afterwards hardened and blunted by contact with the
external world, like the exquisitely sensitive feelings of a
child. The fry may be occasionally seen attached to the
outer folds of the mantle. They appear to be kidneyshaped,
and are of different sizes, or degrees of deve-
lopment.
This species was named, but not described, by Mr.
S. Wood in 1840 as a tertiary fossil ;
and I was fortu-