Old Red Sandstone series, [31], [618].

Onychoteuthis, [462].

Oolite formation, [27].

------ zoophytes of the, [275].

Ophidia, [646], [738].

Ophiura Egertoni, [305].

------- Prattii, [305].

------- serrata, [305].

Ophiuridæ, [303], [304].

Opossum, fossil, [804].