106 DR. C. I. FORSYTH MAJOR ON" PLIOCENE VOLES. [Feb. 18, 



Text-fig. 15. 



F. G. del. 

 Teeth of Voles from Forest Bed and Norwich Crag. 

 Figs. 18-21, 22 a, 23-30, first lower molars, upper view, enlarged. 

 Fi?. 18. Ificrotus, sp., recalling somewhat 31. gregalis ; rootless, left side ; West 

 Eunton (B. M. No. 6987 a, from Savin Coll. No. 1708).— Fig. 19. Microtus 

 nival aides, sp. n., recalling M. nivalis, but smaller and anterior loop more 

 produced : left side ; rootless (B. M. No. 6987 b, from Savin Coll. No. 1708). 

 — Fig. 20. Mimomi/s plioccenictts, same specimen as fig. 15 : left side, enamel 

 islet vanishing. — Fig. 21. Mimomys intermedins, same specimen as fig. 12 ; 

 West Eunton (B. M. No. M 6968 a, from Savin Coll. No. 1692) : left side, 

 cement-spaces closed below, but roots not yet developed. — Fig. 22. Mimomys 

 intermedius, first lower molar, right side, outer aspect ; West Eunton (B. M. 

 No. 6968 b, from Savin Coll. No. 1692) : cement-spaces closed below, but roots 

 not yet developed ; fig. 22 a. Same specimen, upper view ; fig. 22 b. Same 

 specimen, inner aspect. — Fig. 23. 3Iimomi/s netvtoni?. East Eunton; same 

 specimen as fig. 16. — Fig. 24. Mimomys intermedius, right side ; East Eunton 

 (B. M. No. 6967 c, fi-om Savin Coll. No. 465) : cement-spaces, with the ex- 

 ception of the antero-external, still open below. — Fig. 25. Mimomys inter- 

 medius, right side, young ; West Eunton (B. M. No. M 6968 c, from Savin Coll. 

 No. 1692) : cement-spaces narrowing below, but not closed (the lower end of 

 the tooth is incomplete from break). From an inspection of the outer side 

 it becomes evident that by progress of wear the anterior enamel fold would 

 soon have been reduced to an ephemeral enamel islet. — Fig. 26. Mimomys 

 intermedius ?, same specimen as fig. 13, right side ; West Eunton. — Fig. 27. 

 Microtus sp., recalling M. arvalis : left side, rootless ; West Eunton (B. M. 

 No. M6987 c, from Savin Coll. No. 1708).— Fig. 28. Microtus {Pity my s) sp., 

 right side, rootless; West Eunton (B. M. No. M 6987 d, from Savin Coll. 

 No. 1708). Behind the anterior loop follows a transverse loop resulting from 

 the union of the third outer and the fourth inner prism (counting from 

 behind). This loop is separated ft-om the anterior loop by the meeting in the 

 middle line of the third outer and the fourth inner reentrant angle ; features 

 characteristic of the European members of the subgenus Pitymys. — Fig. 29. 

 Mimomys pliocieniaos, young, right side, posterior portion broken oflf ; Norwich 

 Crag, Thorpe (Norw. Castle Mus. No. 971 : Fitch Collection). The antero- 

 external reentrant angle not yet reduced to an enamel islet. Cement-spaces 

 beginning to be closed below. — Fig. 30. Mimomys jplioccenicus, j'oung, right 

 side (Norwich Mus. No. 2708 : from Gurney Collection). " Upper Fresh- 

 water Bed, Ostend." Cement-spaces closed below ; no roots developed. 

 Enamel islet not yet formed. 



