OVULUM. vi) 
To which may be added Conularia, Def. and Amplexus, Sow. 
Fig. 463 to 470. 
ORTHOCER’ATA. BI. The first family of Polythalamacea, Bl. 
containing the genera Belemnites, Conularia, Conilites, Ortho- 
ceras and Baculites. 
ORTHOCERATITES. Auct. Fam. Orthocerata, Lam. and Bl. 
Descr. Straight, conical, divided into numerous chambers by 
simple septa perforated by a central siphon. O. annulata, fig. 464. 
OSTEODESMA. Desh. Awartina rupicola, Lam. 
OSTRA’CEA. (Ostracées, Lam.) A family belonging to the second 
section of the order Conchifera Monomyaria, containing the 
genera Gryphzea, Ostreea, Vulsella, Placuna, Anomia. 
OSTRA’CEA. BI. The first family of the order Lammellibranch- 
iata, Bl. Containing the genera Anomia, Placuna, Harpax, 
Ostreea, (including Dendostrza, Sw.) Gryphzea. To these may 
be added Placunanomia, Brod. and Mulleria. 
OS'TRZEA. Linn. (osrpeor, ostreon, a bone.) Fam. Ostracea, Lam. 
and Bl. Descr. Irregular, inequivalve, generally inequilateral, 
foliaceous, attached by part of the lower valve; hinge sometimes 
slightly crenated, destitute of teeth; with the ligament spread 
upon the lower part of a central triangular area, which is divided ' 
into three parts; upper valve much flatter than the lower; mus- 
cular impressions one in each valve, large, sub-central, sub-orbi- 
cular, with one very minute. Obs. The common oyster is the 
type of this genus, which is abundant in various parts of the 
world. Those which depart furthest from this type are the 
Gryphea, Lam. with a prominent incurved umbo in the lower 
valve. The Dendostrea, Sw. with margins characterized by 
strongly angulated folds, throws out arms from the lower valve, 
by which they are attached to stems of sea-weed, &c. Fig. 180, 
O. edulis. Fig. 181, O. folium. (Dendostrzea, Sw.) Fig. 182, 
Gryphea incurva. Fig. 183, Exogyra conica. 
O'TIDES. Bl. The first order of Scutibranchiata. Bl. containing 
the genera Haliotis and Ancylus. 
O'TION. (azoy, a little ear.) Order. Pedunculated Cirripedes, 
Lam. Descr. Body sub-quadrate, supported on a fleshy pedicle 
with a gaping aperture and two posterior auricular tubes ; valves 
five, separate, two semilunar, placed at the sides of the aperture, 
two terminal very small, one dorsal, minute. Obs. Otion differs 
from Cineras in having two cylindrical posterior tubes, and in the 
extreme minuteness of three out of five of the valves. O. Cuvi- 
erii (Lepas aurita, Lin.) Fig. 43. O. Cuvieri. 
OVATE. (Cvatus.) Egg-shaped, or oval. 
O’'VEOLITHES. Montf. A microscopic shell resembling Bulla. 
OUTER LIP. v. Lasrum. 
O'VULUM. Auct. (Ovum, an egg, dim.) Fam. Convoluta, Lam. 
Angyostomata, Bl. Descr. Ovate, or fusiform, smooth, convo- 
lute; spire covered; aperture narrow, with a canal at each ex- 
