52 E. T. Newton — Sjiermophilus beneath Boulder- Clay. 



from the Fisherton gravels " wbicli have yet to be determined." 

 The specific determination of these SpermopMli seems to have rested 

 almost wholly on the form of the mandibular rami ; but as the Nor- 

 folk specimen has only the teeth of the lower jaw preserved, this 

 mode of determination cannot be adopted. Detailed measurements 

 of the lower jaw and teeth of S. erythrogenoides were made by Dr. 

 Falconer; but only those of the teeth can be made use of in the 

 present instance ; they are thus given in vol. ii. page 452 : " Length 

 of three posterior molars 04 in." [= 10'2 mm.] "Length of line 

 occupied by the four molars 0-52 in," [= 134 mm.] 



Of the eight teeth obtained from the " Arctic Freshwater Bed " 

 six belong to the lower jaw and appear to be the first, second and 

 third cheek-teeth of the right and left sides. The other two teeth 

 are from the upper jaw. The lower teeth are all so much worn that 

 the dentine is exposed over nearly the whole surface, having only a 

 small depression of enamel on the outer side. The enamel border, 

 which in the recent forms stands up as a ridge, is in these teeth 

 broken, or worn away. The forms and proportionate sizes will be 

 best understood from the figures (Plate II. Figs. 3 to 8). The an- 

 terior pair, which are believed to be the fourth pi-emolars, have both 

 lost their fangs, and the broken surface does not show how many 

 each had. The other four lower teeth, which seem to be the first and 

 second true molars of the right and left rami, have each four fangs. 



The space occupied by the three lower teeth on each side is '33 in. 

 (= 8-5 mm.), and the four when altogether probably measured, as 

 nearly as possible, 45 in. (= 11-5 mm.). 



The two upper teeth are less worn, and retain their characteristic 

 cusps and ridges, the black surface being to a great extent covered 

 by a whitish layer of what appears to be much worn enamel ; but of 

 this I cannot be certain. The crown of each tooth is irregularly 

 triangular in outline (Figs. 1, 2), and has one large inner cusp, and 

 three smaller outer ones. A prominent ridge, or rather two ridges, 

 in the form of a horse-shoe, connect the outer and two anterior inner 

 cusps, and thus inclose a deep transverse valley, which is closed on 

 the inner side by the one lai'ge cusp, but opens outwards between 

 the two smaller ones. The hindermost ridge has another cusp about 

 midway between the inner and outer cusps. In front of the horse- 

 shoe ridge there is a secondary valley inclosed by a slight ridge, 

 which forms the anterior boundary of the crown, but this is at a 

 much lower level than the horse-shoe ridge. At the hinder part of 

 the tooth a slight ridge runs down from the large cusp, and curving 

 round joins the hinder outer cusps so as to inclose a slightly depressed 

 space. A small guard is to be traced around the hinder margin of 

 the crown. The antero-posterior extent is about 4 in. (2 5 mm.) 

 The difference in size in the figures is chiefly due to the somewhat 

 different direction in which they were viewed in drawing ihem. 



I have compared these teeth with those of the recent European 

 species in the Brit. Mus. and Royal Coll. of Surgeons. In all these 

 recent forms the lower cheek-teeth are much alike, and although 

 there appears to be some difference in the proportionate sizes of the 



