— 7. _a._ Skull of _Mus arenicola_. — 7. _b._ Molar teeth of upper jaw. — 7. _c._ ditto of lower jaw. — 7. _d._ _Ramus_ of lower jaw. — 8. _a._ Molar teeth of upper jaw of _Mus brachiotis_. — 8. _b._ Two posterior molars of lower jaw. — 9. _a._ Molar teeth of upper jaw of _Mus obscurus_. — 9. _b._ ditto of lower jaw. — 10. _a._ _Ramus_ of lower jaw of _Mus nasutus_. — 11. _a._ Molar teeth of lower jaw of _Mus tumidus_. — 12. _a._ _Ramus_ of lower jaw of _Mus Braziliensis_. — 13. _a._ Molar teeth of upper jaw of _Mus micropus_. — 13. _b._ ditto of lower jaw. — 14. _a._ _Ramus_ of lower jaw of _Mus Galapagoensis_. — 15. _a._ Molar teeth of upper jaw of _Mus griseo-flavus_. — 15. _b._ ditto of lower. — 16. _a._ Molar teeth of upper jaw of _Mus xanthopygus_. — 16. _b._ ditto of lower jaw. — 17. _a._ Molar teeth of upper jaw of _Mus Darwinii_. — 17. _b._ ditto of lower. — 18. _a._ Molar teeth of upper jaw of _Mus Gouldii_. — 18. _b._ ditto of lower. — 19. _a._ Molar teeth of upper jaw of _Mus insularis_. — 19. _b._ ditto of lower jaw. — 19. _c._ Portion of ramus of lower jaw. — 20. _a._ Skull of _Reithrodon chinchilloïdes_—natural size. — 20. _b._ ditto, viewed from beneath. — 20. _c._ ditto, side view. — 20. _d._ _Ramus_ of lower jaw—natural size. — 20. _e._ Molar teeth of upper jaw. — 20. _f._ ditto of lower. — 21. _a._ Skull of _Reithrodon cuniculoïdes_, viewed from beneath. — 21. _b._ ditto, side view of fore part. — 21. _c._ _Ramus_ of lower pair. — 22. _a._ Hinder part of ramus of lower jaw of _Abrocoma Bennettii_. — 23. _a._ Skull of _Abrocoma Cuvieri_, viewed from beneath. — 23. _b._ Lower jaw of ditto, viewed from beneath. — 23. _c._ _Ramus_ of lower jaw, inner side. — 24. _a._ _Ramus_ of lower jaw of _Octodon Cumingii_, inner side. — 25. _a._ Skull of _Didelphis crassicaudata_. — 25. _b._ ditto, viewed from beneath. — 25. _c._ Side view of fore part of skull. — 25. _d._ _Ramus_ of lower jaw, outer side. XXXV. Skulls of various animals. Fig. 1. _a._ Skull of _Desmodus D’Orbignyi_. — 1. _b._ ditto, viewed from beneath. — 1. _c._ ditto, side view. — 1. _d._ Front view of the incisors, and canines of upper jaw magnified. — 1. _e._ Side view of do. and the molar teeth. — 1. _f._ Front view of incisors and canines of lower jaw, magnified. — 1. _g._ Side view of ditto, and molar teeth. — 2. _a._ Skull of _Phyllostoma Grayi_. — 2. _b._ Side view of ditto. — 2. _c._ } Front view of incisors of upper and — 2. _d._ } lower jaws magnified. — 3. _a._ Skull of _Vespertilio Chiloensis_. — 3. _b._ Side view of ditto. — 3. _c._ Front view of upper and lower incisors magnified.