Ortalida, ii. [343]

Orthagoriscus, ii. [457]

Orthalicus, ii. [516]

ORTHIDÆ, ii. [532]

ORTHOCERATIDÆ, ii. [506]

Orthodon, ii. [452]

Orthogonius, ii. [491]

Orthogonys, ii. [98]

Orthonyx, ii. [260]

Orthorhynchus, ii. [108]