214 DR. C. J. FORSYTH MAJOR ON MIOCENE SQUIRRELS. [Feb. 28, 



(4) From the polybuuous molar, as characterized before, have 

 beeu derived the other types of Placental molars, by a gradual 

 transformation of the longitudinal arrangement of cusps into a 

 transverse one {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 Imt 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 polybuuous molar 

 or its derivatives may be " homologous with the reptilian cone," 

 I do not know. 



VI. EXPLANATION OF THE PLATES. 



Plate VIIL 

 Eight superior molars, much magnified, of: — 



Fig. L Sciurus (Eosciurus) indtcus, Tirsl. m,. (B.M. 1203a.) 



2. ScprevosthBesm. mj. (B.M. 5836.) 



3. Sc. lokroidcs, Hodgs. m^. (B.M. 18fi8/4 . 4.3.) 



4. Sc. cveretti, Thos. m.,. (B.M. 1892/9 . 6.8.) 



5. A'ertis (Eoxerus) hosei, Tlios. p^. (B.M. 1892/7 . 19.2.) 



6. A'erus (Eoxerus) insignis, Fr. Ouv. m,. (B.M. 68 c.) 



1. Xents{Protoxerus) stangeri,'SV&i&i[i. m,. (B.M. 515 0.) 



8. Xerus (Protoxeriis) aubmnii, Qv. m^. (B.M. 1875/4 . 30.4.) 



9. Xertis {Atlantoxcrus) gctulus, Gesn. m,. 



10. Xerus erythopus, Geoff. m„. (B.M. 1888/11 .4.4.) 



11. Xerus {Eoxerus) Micaudatas, Gv. mj. (B.M. 1885/8 . 1.272.) 



12. „ ,, Pi- ,, 



13. Anomalurus fraseri, Waterh. pj. (B.M. 555 c.) 



14. AnomalHnis'beecroffi,¥raa. m^. (B.M. 1066 6. 1886/1 . 5.1.) 



15. Xerus (Paraxerus) pi/rropics, Fv. Cuv. m^ (B.M. 897«.) 



16. Xerus {Eoxerus) berdmorei, BIy. (juv.) m^. (B.M. 1878/6 . 17.51.) 



17. „ „ (middle age), mj. (B.M. 1878/6.17.33.) 



18. „ „ (old), m,. (B.M. 1861/4.12.13.) 



19. Pteromys leiwogenys, Temm. mj. (B.M. 656 b.) 



20. Sniuropterus fearsoni, Gr. m.,. (B.M. 1883 «.) 



21. Sciuroptertis horsfcldi, Waterfi., type. m^. (B.M. 1855/12 . 24.102.) 



22. A'erus (Paraxertis) ce^Mpi, Smith, m,. (B.M. 1885/12 . 8.2.) 



23. Xerus (Paraxerus) pyrropus anerythrus, Thos. mj. (B.M. 1890/6. 



8.22.) 



24. Xerus (Paraxerus^ Isabella, Gr. m^. (B.M. 1862/5 . 9.3.) Cameroons. 



Plate IX. 

 Eight inferior molars, much magnified, of : — 



Fig. 1. Sciurus (Eosciurus) indmts, Er.\l. m;. 



2. Ehithrosciunis macrotis, Gr. mj. (B.M. 1888/8 . 13.7.) 



3. Sciurus lokroides, Hodgs. m,. 



4. Sciurus everetti, Thos. m^. 



