Pvn H,i I'UitlS

10 TEREBRATULIDjE.
* Jointed.
Family I. TEREBRATU'LID.E, Gray.
Body oval : arms folded back, and supported either by shelly
processes issuing from the hinge of the lower valve, or by lon-
in that valve : attachment formed
gitudinal septa or partywalls
by a peduncle, which passes through a hole in the upper valve.
Shell longitudinally or transversely oval, more or less con-
vex : skeleton or apophysary system consisting of riband-shaped
plates, which are frequently looped or united : hinge
formed of
two side-teeth in the upper valve, which lock into sockets in
the lower valve : muscular scars slight and seldom visible.
This family is very numerous and diversified in cha-
racter, and it is also widely dispersed both in space and
time. Some of its members occur in every sea, from
the arctic to the antarctic pole ; and its geological
range appears to include all the known strata, from the
Silurian to those which are now in course of formation.
Colonna in 1616 was the first to use the name
Anomia, and applied it to species of Terebratula j and
Linne and other naturalists of the old school also placed
them in the former genus, because they are attached to
extraneous substances by a fibrous tendon passing
through one of the valves of the shell. But although
the analogy holds good to a certain extent, it is not
complete.
In this section of the Brachiopoda the upper
valve, and in Anomia the lower valve is thus perforated,
to say nothing of the very different organization of the
animal and internal structure of the shell. Systematists
are not yet agreed as to the number of genera into
which this large family ought to be divided, nor whether
any or how many subgenera are allowable. Either mode
of distinction, however, is clearly artificial, and used
for the sake of convenient classification. As
merely