MIMOMYS 381 



Explanation of Fio. 105. 



All the specimens figured are from the Upper Freshwater Bod at West 

 Runton, and all are referred to Mimomys majori Hinton. 



1. Left ?»! young; outer view, PI. XV, fig. 12; basal pattern like fig. 14 



below. 



2. Right wij adult; Peat. 



3. Right Wi cement spaces closing; outer view, PI. XV, fig. 6 [Savin 



Coll., No. 9.5.19.2). 



4. Left ?n, young, cement spaces not yet closed; basal pattern like fig. 5; 



outer view, PI. XV, fig. 9 (Savin Coll., No. 9.4.28.1). 



5. Right 7»i adult (Savin Coll., No. 824.1). 



6. Right ?«! voung; outer view, PI. XV, fig. 3 (Savin Coll., No. 9.4.28.2). 



7. Left nil adult; outer view, PI. XV, fig. 2 (Savin Coll., No. 9.5.18.1). 



8. Right 7?!i, cement spaces closing; outer view, PI. XV, fig. 4 (Savin 



Coll., No. 9.4.30.1). 



9. Right m, young; outer view, PI. XV, fig. 11 (Savin Coll., No. 9.5.21.1). 



10. Left ?nj young adult (Savin Coll., No. 823.1). 



11. Right ml adult; outer view, PI. XV, fig. 7 (iS'ai-m Coll., No. 9.4.22.2). 



12. Right ?»! cement spaces closing; outer view, PI. XV, fig. 10 (Savin 



Coll., No. 9.4.22.1). 



13. Left Wj j-oung, pulp cavities open, basal pattern like fig. 14 below; 



outer view, PI. XV, fig. 8 (Savin Coll., No. 9.5.19.1). 



14. Left »H, adult, short roots; "Monkey Gravel," West Runton (G. 



White). 



15. Right nil young; outer view, PI. XV, fig. 5 (Savin Coll., No. 9.4.30.2). 



16. Left »?ii adult (Savin Coll., No. 822.2). 



17. Right wij and Wj adult (3Ius. Pract. Geol., No. G.R. 950C). 



18. Molars of a left mandibular ramus (B.M., No. M. 6966r, Savin Coll.). 



19. Right wii adult (Savin Coll., No. 822.1). 



20. Right ?»! and iiu adult (Savin Coll., No. 823.2). 



21. Left nil adult ; Peat (G. White). 



22. Left ?»! and m^ (G. White). 



specimen proves, is to be regarded as the external vestige of a 

 fourth outer valley. 



Another and probably slightly younger OTj from the West 

 Runton peat (Fig. 1046 and PI. XV, fig. 1) differs from the tooth 

 just described in lacking any trace of the " prism-fold." In this 

 stage of wear the third outer valley is not deeper transversely 

 than are the first and second outer folds behind it; the base 

 of the tooth shows that although the two latter folds would 

 become deeper in adult stages of wear there would be no change 

 in the depth of the third fold. The tubercular cap of the anterior 

 loop is not yet quite worn off, and a minute and ephemeral 

 " fourth outer prism " can be seen. In front of this there 

 is a conspicuous enamel ring or " islet " (iv) placed obliquely 

 on the outer edge of the anterior loop. The lower or outer 

 margin of this islet is formed by a convex swelling answering 

 to the minute tubercle seen in the young tooth described above ; 

 a little below the point where this tubercle subsides a shallow 

 well-defined vertical groove, exactly like that seen in the first 

 .'>pecimen, commences and persists throughout the lower levels 

 of the tooth (PL XV, fig. 1). The " islet " undoubtedly represents 



