CYRTOCERAS (Gr. _kurtos_. crooked; _keras_, horn). A genus of Tetrabranchiate Cephalopods.

CYSTIPHYLLUM (Gr. _kustis_, a bladder; _phullon_, a leaf). A genus of Rugose Corals.

CYSTOIDEA (Gr. _kustis_, a bladder; _eidos_, form). The "Globe-crinoids," an extinct order of _Echinodermata_.

DADOXYLON (Gr. _dadion_, a torch; _xulon_, wood). An extinct genus of Coniferous trees.

DECAPODA (Gr. _deka_, ten; _podes_, feet). The division of _Crustacea_ which have ten feet; also the family of Cuttle-fishes, in which there are ten arms or cephalic processes.

DECIDUOUS (Lat. _decido_, I fall off). Applied to parts which fall off or are shed during the life of the animal.

DEINOSAURIA (Gr. _deinos_, terrible; _saura_, lizard). An extinct order of Reptiles.

DEINOTHERIUM (Gr. _deinos_, terrible; _therion_, beast). An extinct genus of Proboscidean Mammals.

DENDROGRAPTUS (Gr. _dendron_, tree; _grapho_, I write). A genus of Graptolites.

DESMIDIae. Minute fresh-water plants, of a green colour, without a siliceous epidermis.

DIATOMACEae (Gr. _diatemno_, I sever). An order of minute plants which are provided with siliceous envelopes.

DIBRANCHIATA (Gr. _dis_; twice; _bragchia_, gill). The order of _Cephalopoda_ (comprising the Cuttle-fishes, &c.) in which only two gills are present.

DICERAS (Gr. _dis_, twice; _keras_, horn). An extinct genus of Bivalve Molluscs.

DICTYONEMA (Gr. _diktuon_, a net; _nema_, thread). An extinct genus of _Polyzoa_.

DICYNODONTIA (Gr. _dis_, twice; _kuon_, dog; _odous_, tooth).

An extinct order of Reptiles.

DIDYMOGRAPTUS (Gr. _didumos_, twin; _grapho_, I write). A genus of Graptolites.

DIMORPHODON (Gr. _dis_, twice; _morphe_, shape; _oduos_, tooth).

A genus of Pterosaurian reptiles.

DINICHTHYS (Gr. _deinos_, terrible; _ichthus_, fish). An extinct genus of Fishes.

DINOCERAS (Gr. _deinos_, terrible; _keras_, horn). An extinct genus of Mammals.

DINOPHIS (Gr. _deinos_, terrible; _ophis_, snake). An extinct genus of Snakes.

DINORNIS (Gr. _deinos_, terrible; _ornis_, bird). An extinct genus of Birds.

DIPLOGRAPTUS (Gr. _diplos_, double; _grapho_, I write). A genus of Graptolites.

DIPNOI (Gr. _dis_, twice; _pnoe_, breath). An order of Fishes, comprising the Mud-fishes, so called in allusion to their double mode of respiration.

DIPROTODON (Gr. _dis_, twice; _protos_, first; _odous_, tooth).

A genus of extinct Marsupials.

DIPTERA (Gr. _dis_, twice; _pteron_, wing). An order of Insects characterised by the possession of two wings.

DISCOID (Gr. _diskos_, a quoit; _eidos_, form). Shaped like a round plate or quoit.

DOLOMITE (named after M. Dolomieu). Magnesian limestone.

DORSAL (Lat. _dorsum_, the back). Connected with or placed upon the back.

DROMATHERIUM (Gr. _dromaios_, nimble; _therion_, beast). A genus of Tria.s.sic Mammals.

DRYOPITHECUS (Gr. _drus_, an oak; _pithekos_, an ape). An extinct genus of Monkeys.

ECHINODERMATA (Gr. _echinos_; and _derma_, skin). A cla.s.s of animals comprising the Sea-urchins, Star-fishes, and others, most of which have spiny skins.

ECHINOIDEA (Gr. _echinos_; and _eidos_, form). An order of _Echinodermata_, comprising the Sea-urchins.

EDENTATA (Lat. _e_, without; _dens_, tooth). An order of _Mammalia_ often called _Bruta_.

EDENTULOUS. Toothless, without any dental apparatus. Applied to the mouth of any animal, or to the hinge of the Bivalve Molluscs.

ELASMOBRANCHII (Gr. _elasma_, a plate; _bragchia_, gill). An order of Fishes, including the Sharks and Rays.

ENALIOSAURIA (Gr. _enalios_, marine; _saura_, lizard), Sometimes employed as a common term to designate the extinct Reptilian orders of the _Ichthyosauria_ and _Plesiosauria_.

EOCENE (Gr. _eos_, dawn; _kainos_, new or recent). The lowest division of the Tertiary rocks, in which species of existing sh.e.l.ls are to a small extent represented.

EOPHYTON (Gr. _eos_, dawn; _phuton_, a plant). A genus of Cambrian fossils, supposed to be of a vegetable nature.

EOZOoN (Gr. _eos_, dawn; _zoon_, animal). A genus of chambered calcareous organisms found in the Laurentian and Huronian formations.

EQUILATERAL (Lat. _oequus_, equal; _latus_, side). Having its sides equal. Usually applied to the sh.e.l.ls of the _Brachiopoda_.

When applied to the spiral sh.e.l.ls of the _Foraminifera_, it means that all the convolutions of the sh.e.l.l lie in the same plane.

EQUISETACEae (Lat. _equus_, horse; _seta_, bristle). A group of Cryptogamous plants, commonly known as "Horse-tails."

EQUIVALVE (Lat. _oequus_, equal; _valvoe_, folding-doors). Applied to sh.e.l.ls which are composed of two equal pieces or valves.

ERRANTIA (Lat. _erro_, I wander). An order of _Annelida_, often called _Nereidea_, distinguished by their great locomotive powers.

EUOMPHALUS (Gr. _eu_, well; _omphalos_, navel). An extinct genus of Univalve Molluscs.

EURYPTERIDA (Gr. _eurus_, broad; _pteron_, wing). An extinct sub-order of _Crustacea_.

EXOGYRA (Gr. _exo_, outside; _guros_, circle). An extinct genus of Oysters.