Plate I.--Fig. 1, Restoration of upper side of the elongated species of _Pterichthys_ (_P. oblongus_,) referred to in page 47. Fig. 2, _Pterichthys Milleri_. Fig. 3, Part of tail of elongated species, showing portions of the original covering of rhomboidal scales. Fig. 4, Tubercles of _Pterichthys_ magnified. Plate II.--Fig. 2, Restoration of under side of _Pterichthys oblongus_. Fig. 1, A second specimen of _Pterichthys Milleri_. Fig. 3, Portion of wing, natural size. Plate III.--Fig. 1, _Coccosteus cuspidatus_. Fig. 2, Impression of inner surface of large dorsal plate. Fig. 3, Abdominal lozenge-shaped plate. Fig. 4, Portion of jaw, with teeth. Plate IV.--Fig. 1, Restoration of _Osteolepis major_. Fig. 2, Scales from the upper part of the body magnified. Fig. 3, Large defensive scale which runs laterally along all the single fins. Fig. 4, Under side of scale, showing the attaching bar. Fig. 5, Enamelled and punctulated jaw of the creature. Fig. 6, Magnified portion of fin, showing the enamelled and punctulated rays. Plate V.--Fig. 1, _Dipterus macrolepidotus_. This figure serves merely to show the place of the fins and the general outline of the ichthyolite. All the specimens the writer has hitherto examined fail to show the minuter details. Fig. 2, _Glyptolepis leptopterus_. Fig. 3, Single scale of the creature, showing its rustic style of ornament. Fig. 4, Scale with a nail-like attachment. Fig. 5, Under side of scale. Fig. 6, Magnified portion of fin. Fig. 7, Shells of the Old Red Sandstone. Plate VI.--Fig. 1, _Cheirolepis Cummingiæ_. Fig. 2, Magnified scales. Fig. 3, Magnified portion of fin. Plate VII.--Fig. 1, _Cheiracanthus microlepidotus_. Fig. 2, Magnified scales. Figs. 3, 4, 5, 6, 7, 8, Vegetable impressions of the Old Red Sandstone. Plate VIII.--Fig. 1, _Diplacanthus longispinus_. Fig. 2, _Diplacanthus striatus_. Fig. 3, Magnified scales of fig. 1. Fig. 4, Spine of fig. 2, slightly magnified. Plate IX.--Fig. 1, One of the tail flaps of the gigantic Crustacean of Forfarshire. Fig. 2, Reticulated markings of Carmylie. Plate X.--Fig. 1, _Cephalaspis Lyellii_, copied from Lyell's _Elements of Geology_, Fig. 2, _Holoptychius nobilissimus_, copied on a greatly reduced scale from Murchison's _Silurian System_, Fig. 3, Scale of _Holoptychius_, natural size. Fig, 4, Tooth of ditto, also natural size. These last drawn from specimens in the collection of Mr. Patrick Duff, of Elgin. DIRECTIONS TO THE BINDER. Sheet of Sections to front Title-Page. Plate I. to front page 44 II. " " " 46 III. " " " 48 IV. " " " 66 V. " " " 72 VI. " " " 78 VII. " " " 82 VIII. " " " 84 IX. " " " 136 X. " " " 154 NEW WALKS IN AN OLD FIELD; OR, THE OLD RED SANDSTONE. CHAPTER I.