Orbicula, [392].

Orbitoides Mantelli, [346].

Oreston, near Plymouth, [810].

Organic remains, nature of, [37].

Ornithoidichnites, [768].

Ornitholites, [759], [763].

Orthacanthus, [581].

Orthis, [392].

Orthoceratidæ, [469], [474].

Orthoceras conicum, [475].