—— obscurus. XVI. —— longipilis. XVII. —— xanthorhinus. —— nasutus. XVIII. —— tumidus. XIX. —— Braziliensis. XX. —— micropus. XXI. —— griseo-flavus. XXII. —— xanthopygus. XXIII. —— Darwinii. XXIV. —— Galapagoensis. XXV. —— fuscipes. XXVI. Reithrodon cuniculoïdes. XXVII. —— chinchilloïdes. XXVIII. Abrocoma Bennettii. XXIX. —— Cuvieri. XXX. Didelphis crassicaudata. XXXI. —— elegans. XXXII. —— brachyura. XXXIII. Skulls, and molar teeth of various species of Rodents. Fig. 1. _a._ Skull of _Abrocoma Cuvieri_—natural size. — 1. _b._ Side view of ditto. — 1. _c._ _Ramus_ of lower jaw—outer side. — 1. _d._ Lower jaw seen from above. — 1. _e._ Molar teeth of the upper jaw magnified. — 1. _f._ ditto of lower jaw. — 2. _a._ Skull of _Reithrodon cuniculoïdes_. — 2. _b._ Incisors of the upper jaw magnified. — 2. _c._ Molar teeth of the upper jaw magnified. — 2. _d._ ditto of the lower jaw. — 2. _e._ ditto of upper jaw of a younger specimen. — 3. _a._ Portion of a skull of _Mus Braziliensis_. — 3. _b._ ditto, view of palate. — 3. _c._ Molar teeth of the upper jaw magnified. — 3. _d._ ditto of lower jaw. — 4. _a._ Molar teeth of lower jaw of _Reithrodon typicus_ magnified. — 5. _a._ Molar teeth of the upper jaw of _Mus canescens_. — 5. _b._ ditto of under jaw. — 5. _c._ Skull of ditto. — 5. _d._ Posterior molar of the lower jaw more worn than in 5. _b._ — 6. _a._ Molar teeth of the lower jaw of _Mus longipilis_. — 6. _b._ Molar teeth of the upper jaw. — 7. _a._ Skull of _Mus nasutus_. — 7. _b._ Molar teeth of upper jaw. — 7. _c._ ditto of lower jaw. — 8. _a._ Skull of _Mus Galapagoensis_. — 8. _b._ Molar teeth of upper jaw. — 8. _c._ ditto of lower jaw. XXXIV. Skulls and molar teeth of various species of Rodents, &c. Fig. 1. _a._ Skull of _Mus longicaudatus_—natural size. — 1. _b._ Molar teeth of upper jaw of ditto. — 1. _c._ ditto of lower jaw. — 1. _d._ _Ramus_ of lower jaw—natural size. — 2. _a._ Skull of _Mus elegans_—natural size. — 2. _b._ Molar teeth of upper jaw. — 2. _c._ ditto of lower jaw. — 3. _a._ Skull of _Mus bimaculatus_—nat. size. — 3. _b._ Molar teeth of upper jaw. — 3. _c._ ditto of lower jaw. — 3. _d._ _Ramus_ of lower jaw—natural size. — 4. _a._ Skull of _Mus gracilipes_. — 4. _b._ Molar teeth of upper jaw. — 4. _c._ ditto of lower jaw. — 4. _d._ View of the under side of the tarsus. — 5. _a._ First and second molar teeth of upper jaw of _Mus flavescens_. — 5. _b._ Two posterior molar teeth of the lower jaw of ditto. — 6. _a._ Molar teeth of the upper jaw of _Mus Magellanicus_. — 6. _b._ ditto of lower jaw.