ion
of a hard shell or crust, which they cast periodically.

CRYPTOGAMS (Gr. _kruptos_, concealed; _gamos_, marriage). A division
of plants in which the organs of reproduction are obscure and
there are no true flowers.

CTENACANTHUS (Gr. _kteis_, a comb; _akantha_, a thorn). A genus
of fossil fishes, named from its fin-spines.

CTENOID (Gr. _kteis_, a comb; _eidos_, form). Applied to those
scales of fishes the hinder margins of which are fringed with
spines or comb-like projections.

CURSORES (Lat. _curro_, I run). An order of _Aves_, comprising
birds destitute of the power of flight, but formed for running
vigorously (_e.g._, the Ostrich and Emeu).

CUSPIDATE. Furnished with small pointed eminences or "cusps."

CYATHOCRINUS (Gr. _kuathos_, a cup; _krinon_, a lily). A genus
of Crinoids.

CYATHOPHYLLUM (Gr. _kuathos_, a cup; _phullon_, a leaf). A genus
of Rugose Corals.

CYCLOID (Gr. _kuklos_, a circle; _eidos_, form). Applied to those
scales of fishes which have a regularly circular or elliptical
outline with an even margin.

CYCLOPHTHALMUS (Gr. _kuklos_, a circle; _ophthalmos_, eye). A
genus of fossil Scorpions.

CYCLOSTOMI (Gr. _kuklos_, and _stoma_, mouth). Sometimes used
to designate the Hag-fishes and Lampreys, forming the order
_Marsipobranchii_.

CYPRAEA (a name of Venus). The genus of Univalve Molluscs comprising
the Cowries.

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