PLATE I. Cranium of _Toxodon Platensis_, nat. size, basal view, with the sixth molar, right side upper jaw, and grinding surface of the seventh molar left side. II. Cranium of _Toxodon Platensis_, side view. III. Ditto, upper view. IV. Ditto, back view, with two views of the sixth molar, right side, upper jaw. V. Fragment of lower jaw, and teeth of _Toxodon Platensis_. VI. Cervical vertebræ of the _Macrauchenia Patachonica_. VII. Ditto, ditto, and of _Auchenia Llama_. VIII. Lumbar vertebræ of the _Macrauchenia Patachonica_. _a._ Medium convex articular surface joining the body of the sacrum. _b._ Lateral concavities joining the transverse processes of the _b._ sacrum. _c._ Ossified ligament of an anchylosed lumbar vertebra. IX. Fig. 1 and 2. Fragments of the Scapula. Fig. 3. Distal end of the femur of _Macrauchenia Patachonica_. X. Proximal ends of the anchylosed radius and ulna of _Macrauchenia Patachonica_. XI. Bones of the right fore-foot, _Macrauchenia Patachonica_. XII. Femur, _Macrauchenia Patachonica_. XIII. Anchylosed tibia and fibula, _Macrauchenia Patachonica_. XIV. Right astragalus, _Macrauchenia Patachonica_. XV. Fig. 1. External metatarsal bone of the right hind-foot. Fig. 2. Proximal end of internal metacarpal bone, right fore-foot. Fig. 3 and 4. Proximal end of middle metacarpal bone. Fig. 5. Proximal end of external metacarpal bone, right fore-foot, _Macrauchenia Patachonica_. XVI. Fragment of cranium of the _Glossotherium_. Fig. 1. Side view. Fig. 2. Base view. Fig. 3. Inside view, all half natural size. Fig. 4. Os tympanicum, natural size. XVII. Fig. 1. _Megalonyx Jeffersonii._ Fig. 2. _Megalonyx laqueatus._ Fig. 3 and 4. _Mylodon Harlani._ Fig. 5. _Mylodon Darwinii._ XVIII. Lower jaw of the _Mylodon Darwinii_. XIX. Fig. 1. Side view of the lower jaw. Fig. 2 and 3. Last molar tooth. Fig. 4. Front view of the symphysis of the lower jaw, _Mylodon Darwinii_. XX. Portion of the skeleton of the _Scelidotherium leptocephalum_. XXI. Fig. 1. Side view of the cranium. Fig. 2. Back view of the cranium. Fig. 3, 4, and 5, anterior molar, upper jaw _Scelidotherium_. XXII. Upper view of the cranium of the _Scelidotherium_. XXIII. Fig. 1. Inside view of cranium. Fig. 2. Articular surface for the lower jaw. Fig. 3. Section of upper jaw and molar teeth. Fig. 4. Section of lower jaw and molar teeth, _Scelidotherium_. XXIV. Cervical and anterior dorsal vertebræ of. Fig. 1. _Scelidotherium._ Fig. 2. _Orycteropus._ Fig. 3. _Dasypus._ Fig. 4.