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connects together the various chambers of the shell of certain
_Cephalopoda_ (_e.g._, the Pearly Nautilus).

SIRENIA (Gr. _seiren_. a mermaid). The order of _Mammalia_ comprising
the Dugongs and Manatees.

SIVATHERIUM (_Siva_, a Hindoo deity; Gr. _therion_, beast). An
extinct genus of Hoofed Quadrupeds.

SOLIDUNGULA (Lat. _solidus_, solid; _ungula_, a hoof). The group
of Hoofed Quadrupeds comprising the Horse, Ass, and Zebra, in
which each foot has only a single solid hoof. Often called
_Solipedia_.

SPHENOPTERIS (Gr. _sphen_, a wedge; _pteris_, a fern). An extinct
genus of ferns.

SPICULA (Lat. _spicidum_, a point). Pointed needle-shaped bodies.

SPIRIFERA (Lat. _spira_, a spire or coil; _fero_, I carry). An
extinct genus of Brachiopods, with large spiral supports for
the "arms."

SPIRORBIS (Lat. _spira_, a spire; _orbis_, a circle). A genus
of tube-inhabiting Annelides, in which the shelly tube is coiled
into a spiral disc.

SPONGIDA (Gr. _spoggos_, a sponge). The division of _Protozoa_
commonly known as sponges.

STALACTITES (Gr. _stalasso_, I drop). Icicle-like encrustations
and deposits of lime, which hang from the roof of caverns in
limestone.

STALAGMITE (Gr. _stalagma_, a drop). Encrustations of lime formed
on the floor of caverns which are hollowed out of limestone.

STIGMARIA (Gr. _stigma_, a mark made with a pointed instrument).
A genus founded on the roots of various species of _Sigillaria_.

STRATUM (Lat. _stratus_, spread out; or _stratum_, a thing spread
out). A layer of rock.

STROMATOPORA (Gr. _stroma_, a thing spread out; _paras_, a passage
or pore). A Palaeozoic genus of _Protozoa_.

STROPHOHENA (Gr. _strophao_, I twist; _mene_, moon). An extinct
genus of Brachiopods.

SUB-CALCAREOUS. Somewhat calcareous.

SUB-CENTRAL. Nearly central, but not quite.

SUTURE (Lat. _suo_, I sew). The line of junction of two parts
which are immovably connected together. Applied to the line where
the whorls of a univalve shell join one another; also to the lines
made upon the exterior of the shell of a chambered _Cephalopod_
by the margins of the septa.

SYRINGOPORA (Gr. _surigx_, a pipe; _poros_, a pore). A genus of
Tabulate Corals.

TABULAE. (Lat. _tabula_, a tablet). Horizontal plates or floors
found in some Corals, extending across the cavity of the "theca"
from side to side.

TEGUMENTARY (Lat. _tegumentum_, a covering). Connected with the
integument or skin.

TELEOSAURUS (Gr. _tel