er_. Dorsal valve, showing calcareous spiral coils.

6. _Orthis calligramma_.

7. _Leptaena transversalis_. A, ventral, B, dorsal valve.

8. _Productus horridus_.

9. _Lingula pyramidata_ (after Morse).

10. _Discinisca lamellosa_.

11. _Crania anomala_ Interior of dorsal valve, showing muscular
impressions and labial appendages.]

The soft body of the Brachiopod is in all cases protected by a shell
composed of two distinct valves; these valves are always, except in
cases of malformation, equal-sided, but not equivalved. The valves are,
consequently, essentially symmetrical, which is not the case with the
Lamellibranchiata,--so much so, that certain Brachiopod shells were
named _Lampades_, or lamp shells, by some early naturalists; but while
such may bear a kind of resemblance to an antique Etruscan lamp, by far
the larger number in no way resemble one. The shell is likewise most
beautiful in its endless shapes and variations. In some species it is
thin, semi-transparent and glassy, in others massive. Generally the
shell is from a quarter of an inch to about 4 in. in size, but in
certain species it attains nearly a foot in breadth by something less in
length, as is the case with _Productus giganteus_. The valves are also
in some species very unequal in their respective thickness, as may be
seen in _Productus_ (_Daviesiella_)[1] _llangollensis_, _Davidsonia
verneuilii_, &c., and while the space allotted to the animal is very
great in many species, as in _Terebratula sphaeroidalis_, it is very
small in others belonging to _Strophomena_, _Leptaena_, _Chonetes_, &c.
The ventral valve is usually the thickest, and in some forms is six or
seven times as great as the opposite one. The outer surface of many of
the species presents likewise the most exquisite sculpture, heightened
by brilliant shades, or spots of green, red, yellow and bluish black.
Traces of the original colour have also been preserved in some of the
fossil forms; radiating bands of a reddish tint have been often seen in
well-preserved examples of _Terebratula_ (_Dielasma_) _hastata_, _T_.
(_Dielasma_) _sacculus_, _T. communis_, _T. biplicata_, and of several
others. Some specimens of _T. carnea_ are of a beautiful pale pink
colour when first removed from their matrix, and E. Deslongchamps has
described the tint of several Jurassic species.

The valves are distinguished as _dorsal_ and _ventral_. The ventral
valve is usually the larger, an