ANOPLOTHERIDAE (Gr. anoplos, unarmed; ther, beast).  A family of Tertiary Ungulates.

ANOURA (Gr. a, without; oura, tail).  The order of Amphibia comprising the Frogs and Toads, in which the adult is destitute of a tail.  Often, called Batrachia.

ANTENNAE (Lat. antenna, a yard-arm).  The jointed horns or feelers possessed by the majority of the Articulata.

ANTENNULES (dim. of Antennoe).  Applied to the smaller pair of antennae in the Crustacea.

ANTHRACOSAURUS (Gr. anthrax, coal; saura, lizard).  A genus of Labyrinthodont Amphibians.

ANTHRAPALAEMON (Gr. anthrax, coal; paloemon, a prawn—­originally a proper name).  A genus of long-tailed Crustaceans from the Coal-measures.

ANTLERS.  Properly the branches of the horns of the Deer tribe (Cervidoe), but generally applied to the entire horns.

APIOCRINIDAE (Gr. apion, a pear; krinon, lily).  A family of Crinoids—­the “Pear-encrinites.”

APTERYX (Gr. a, without; pterux, a wing).  A wingless bird of New Zealand, belong to the order Cursores.

AQUEOUS (Lat. aqua, water).  Formed in or by water.

ARACHNIDA (Gr. arachne, a spider).  A class of the Articulata, comprising Spiders, Scorpions, and allied animals.

ARBORESCENT.  Branched like a tree.

ARCHAEOCIDARIS (Gr. archaios, ancient; Lat. cidaris, a diadem). 
A Palaeozoic genus of Sea-urchins, related to the existing Cidaris.

ARCHAEOCYATHUS (Gr. archaios, ancient; kuathos, cup).  A genus of Palaeozoic fossils allied to the Sponges.

ARCHAEOPTERYX (Gr. archaios, ancient; pterux, a wing).  The singular fossil bird which alone constitutes the order of the Saururoe.

ARCTOCYON (Gr. arctos, bear; kuon, dog).  An extinct genus of Carnivora.

ARENACEOUS.  Sandy, or composed of grains of sand.

ARENICOLITES (Lat. arena, sand; colo, I inhabit).  A genus founded on burrows supposed to be formed by worms resembling the living Lobworms (Arenicola).

ARTICULATA (Lat. articulus, a joint).  A division of the animal kingdom, comprising Insects, Centipedes, Spiders, and Crustaceans, characterised by the possession of jointed bodies or jointed limbs.  The term Arthropoda is now more usually employed.

ARTIODACTYLA (Gr. artios, even; daktulos, a finger or toe).  A division of the hoofed quadrupeds (Ungulata) in which each foot has an even number of toes (two or four).

ASAPHUS (Gr. Asaphes, obscure).  A genus of Trilobites.

ASCOCERAS (Gr. askos, a leather bottle; keras, horn).  A genus of Tetrabranchiate Cephalopods.

ASIPHONATE.  Not possessing a respiratory tube or siphon. (Applied to a division of the Lamellibranchiate Molluscs.)