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 Triassic Mammals.

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

ECHINODERMATA (Gr. _echinos_; and _derma_, skin). A class 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. _