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Show 214 DR. C. J. FORSYTH MAJOR ON MIOCENE SQUIRRELS. [Feb. 28, (4) From the polybunous molar, as characterized before, have been derived the other types of Placental molars, by a gradual transformation of the longitudinal arrangement of cusps into a transverse oue (Chiastotaxis), and by a prevailing development of a few cusps-a sort of Oligarchy-as well as by the fusion and suppression of others, several of which are, however, maintained with great persistency in a secondary condition. (5) In the upper molars two outer cusps and one or two inner cusps are usually the most developed. (6) The truly"tritubercular molar is but a very specialized stage, which is often preceded, not followed, by Riitimeyer's trigonodont • type. (7) The supposition that the so-called heel or talon of inferior molars is a later development, is an arbitrary one, disproved by facts. (8) Which of all the cusps of the primitive polybunous molar or its derivatives may be " homologous with the reptilian cone," I do not know. VI. EXPLANATION OF THE PLATES. PLATE VIII. Right superior molars, much magnified, of:- Fig. 1. Sciurus (Eosciurus) indicus, Erxl. m r (B.M. 1203a.) 2. Sc. prevosti, Desm. mv (B.M. 5836.) 3. Sc. lokroides, Hodgs. n^. (B.M. 1868/4 . 4.3.) 4. Sc. everetti, Thos. m2. (B.M. 1892/9 . 6.8.) 5. Xerus (Eoxerus) hosei, Thos. pr (B.M. 1892/7 .19.2.) 6. Xerus (Eoxerus) insignis, Fr. Cuv. rur (B.M. 68 c.) 7. Xerus (Protoxerus) stangeri, Waterh. m,. (B.M. 515 C.) 8. Xerus (Protoxerus) aubinnii, Gr. m,. (B.M. 1875/4 .30.4.) 9. Xerus (Atlantoxerus) qetulus, Gesn. m2. 10. Xerus erythopus, Geoff. m2. (B.M. 1888/11 .4.4.) 11. Xerus (Eoxerus) laticaudatus, Gr. m r (B.M. 1885/8. 1.272.) 12. „ ,, PJ. ,, 13. Anomalurus fraseri, Waterh. p r (B.M. 555 c.) 14. Anomalurus'beecrofti, Fra,s. m,. (B.M. 1066 6. 1886/1. 5.1.) 15. Xerus (Paraxerus) pyrropus, Fr. Cuv. mv (B.M. 897a.) 16. Xerus (Eoxerus) berdmorei, Bly. (juv.) m1. (B.M. 1878/6 .17.51.) 17. „ „ (middle age). m r (B.M. 1878/6.17.33.) 18. „ „ (old). m r (B.M. 1861/4.12.13.) 19. Pteromys leucogenys, Temm. m r (B.M. 556 b.) 20. Sciuropterus pearsoni, Gr. m2. (B.M. 1883 a.) 21. Sciuropterus horsfieldi, Waterh., type. mv (B.M. 1855/12 .24.102.) 22. Xerus (Paraxerus) cepapi, Smith. m r (B.M. 1885/12 . 8.2.) 23. Xerus (Paraxerus) pyrropus anerythrus, Thos. m1. (B.M. 1890/6. 8.22.) 24. Xerus (Paraxerus) isabella, Gr. m2. (B.M. 1862/5.9.3.) Cameroons. PLATE IX. Right inferior molars, much magnified, of:- Fig. 1. Sciurus (Eosciurus) indicus, Erxl. m r 2. Ehithrosciurus macrotis, Gr. mlt (B.M. 1888/8 .13.7.) 3. Sciurus Wcroides, Hodgs. mv 4. Sciurus everetti, Thos. m2. |
