, a column; _spoggos_,
a sponge). A genus of Silurian Sponges.

ATHYRIS (Gr. _a_, without; _thura_, door). A genus of Brachiopods.

ATRYPA (Gr. _a_, without; _trupa_, a hole). A genus of Brachiopods.

AVES (Lat. _avis_, a bird). The class of the Birds.

AVICULA (Lat. a little bird). The genus of Bivalve Molluscs
comprising the Pearl-oysters.

AXOPHYLLUM (Gr. _axon_, a pivot; _phullon_, a leaf). A genus of
Rugose Corals.

AZOIC (Gr. _a_, without; _zoe_, life). Destitute of traces of
living beings.

BACULITES (Lat. _baculum_, a staff). A genus of the _Ammonitidoe_.

BALAENA (Lat. a whale). The genus of the Whalebone Whales.

BALANIDAE (Gr. _balanos_, an acorn). A family of sessile _Cirripedes_,
commonly called "Acorn-shells."

BATRACHIA (Gr. _batrachos_, a frog). Often loosely applied to
any of the _Amphibia_, but sometimes restricted to the Amphibians
as a class, or to the single order of the _Anoura_.

BELEMNITIDAE (Gr. _belemnon_, a dart). An extinct group of
Dibranchiate Cephalopods, comprising the Belemnites and their
allies.

BELEMNOTEUTHIS (Gr. _belemnon_, a dart; _teuthis_, a cuttle-fish).
A genus allied to the Belemnites proper.

BELINURUS (Gr. _belos_, a dart; _oura_, tail). A genus of fossil
King-crabs.

BELLEROPHON (Gr. proper name). A genus of oceanic Univalves
(_Heteropoda_).

BELOTEUTHIS (Gr. _belos_, a dart; _teuthis_, a cuttle-fish). An
extinct genus of Dibranchiate Cephalopods.

BEYRICHIA (named after Prof. Beyrich). A genus of Ostracode
Crustaceans.

BILATERAL. Having two symmetrical sides.

BIMANA (Lat. _Bis_, twice; _manus_, a hand). The order of _Mammalia_
comprising man alone.

BIPEDAL (Lat. _bis_, twice; _pes_, foot). Walking upon two legs.

BIVALVE (Lat. _bis_, twice; _valvoe_, folding-doors). Composed of
two plates or valves; applied to the shell of the _Lamellibranchiata_
and _Brachiopoda_, and to the carapace of certain _Crustacea_.

BLASTOIDEA (Gr. _blastos_, a bud; and _eidos_, form). An extinct
order of _Echinodermata_, often called _Pentremites_.

BRACHIOPODA (Gr. _brachion_, an arm; _pous_, the foot). A class
or the _Molluscoida_, often called "Lamp-shells," characterised
by possessing two fleshy arms continued from the sides of the
mouth.

BRACHYURA (Gr. _brachus_, short; _oura_, tail). A tribe of the
Decapod _Crustaceans_ with short tails (_i.e._, the Crabs).

BRADYPODIDAE. (Gr. _bradus_, slow; _podes_, feet). The family of
_Edentata_ comprising the Sl