GLOSSARY. 389 
NATATORES (Lat. xare, to swim). The order of the Swimming Birds. 
NatatTory (Lat. nare, to swim). Formed for swimming. 
NavtTILorD. Resembling the shell of the Nautilus in shape. 
NERVURES (Lat. nervus, a sinew). The ribs which support the membranous 
wings of insects. 
NEUROPTERA (Gr. neuron, a nerve ; pteron, a wing). An order of Insects char- 
acterised by four membranous wings with numerous reticulated nervures 
(e.g., Dragon-tlies). 
NEUROPTERIS (Gr. neuron, a nerve; pteris, a fern). An extinct genus of 
Ferns. 
NOTHOSAURUS (Gr. nothos, spurious ; sawra, lizard). A geuusof Plesiosaurian 
Reptiles. 
NOTOCHORD (Gr. notos, back ; chorde, string). A cellular rod which is devel- 
oped in the embryo of Vertebrates immediately beneath the spinal cord, and 
which is usually replaced in the adult by the vertebral column. Often it is 
spoken of as the ‘‘ chorda dorsalis.’’ 
NUDIBRANCHIATA (Lat. nudus, naked; and Gr. bragchia, gill). An order of 
the Gasteropoda in which the gills are naked. 
NUMMULINA (Lat. nwmmus, a coin). A genus of Foraminifera, comprising the 
coin-shaped ‘‘ Nummulites.” 
OBOLELLA (Lat. dim. of obolus, a small coin). An extinct genus of Brachio- 
pods. 
OccIPITAL. Connected with the occiput, or the back part of the head. 
OcEANIC. Applied to animals which inhabit the open ocean (= pelagic). 
Ses (Gr. odous, tooth; pteruz, wing). An extinct genus of 
irds, 
ODONTORNITHES (Gr. odous, tooth; ornis, bird). The extinct order of Birds, 
comprising forms with distinct teeth in sockets. 
OLIGOCENE (Gr. oligos, few; kainos, new). A name used by many Continental 
geologists as synonymous with the Lower Miocene. 
OpHIDIA (Gr. ophis, a serpent). The order of Reptiles comprising the Snakes. 
OPHIUROIDEA (Gr. ophis, snake ; oura, tail ; eidos, form). An order of Echino- 
dermata, comprising the Brittle-stars and Sand-stars. 
ORNITHOSCELIDA (Gr. ornis, bird; skelos, leg). Applied by Huxley to the 
Deinosaurian Reptiles, together with the genus Compsognathus, on account 
of the bird-like character of their hind-limbs. 
OrTHIS (Gr. orthos, straight). A genus of Brachiopods, named in allusion to the 
straight hinge-line. 
ORTHOCERATIDA (Gr. orthos, straight ; keras, horn). A family of the Nauw- 
tilide, in which the shell is straight, or nearly so. 
ORTHOPTERA (Gr. orthos, straight ; pteron, wing). An order of Insects. 
OsTEOLEPIS (Gr. osteon, bone; lepis, scale). An extinct genus of Ganoid 
Fishes. 
Ostracopa (Gr. ostrakon, a shell). An order of small Crustaceans which are 
enclosed in bivalve shells. 
Oropus (Gr. ota, ears ; odous, tooth). An extinct genus of Sharks. 
OUDENODON (Gr. owden, none ; odous, tooth). A genus of Dicynodont Rep- 
tiles. 
OvrBos (Lat. ovis, sheep ; bos, ox). The genus comprising the Musk-ox. 
PACHYDERMATA (Gr. pachus, thick; derma, skin). An old Mammalian order 
constituted by Cuvier for the reception of the Rhinoceros, Hippopotamus, 
Elephant, &c. 
PaL@masTER (Gr. palaios, ancient; aster, star). An extinct genus of Star- 
tishes. 
PaLmocarRis (Gr. palaios, ancient ; karis, shrimp). An extinct genus of Deca- 
pod Crustaceans. 
PALMOLITHIC (Gr. palaios, ancient; lithos, stone). Applied to the rude stone 
implements of the earliest known races of men, to the men who made these 
implements, or to the period at which they were made. 
