192 



Mr. M. A. C. Hinton on 



Measurements of navicular 

 (millimetres). 



Trogontherium. 

 Forest Bed: W. Runtou. 



Absolute. Reductions. 



Antero-posterior diameter ...... 



Transverse width in front 



,, „ behind 



Width of astragaleau facette .... 



„ facette for cun. Ill 



,, ), ^ „ 11. • • • ■ 



Antero-posterior diameter of fa- 

 cette for cun. Ill 



Antero-posterior length of cuboid 

 facette j 



Height of cuboid facette at post.- 

 external corner of facette for 

 cun. in 1 



Height of cuboid facette behind . 



Least distance between facette for 

 cun. III. and front edge of 

 proximal surface ' 



Height of spur behind 



19-7 



J 5-7 



7-1 



11-7 



8-6 



6-G 



6-8 



12-0 



5-0 

 0-G 



51 

 7-3 



100 



79-8 

 36-1 

 59-4 

 43-7 

 33-5 



34-6 



Gl 



2o-4 

 33-5 



25-9 

 37-1 



168 



134 

 GO-8 

 100 

 73-0 

 56-4 



58-2 



102 



42-8 

 56-4 



43G 

 62-4 



' Castor. 

 Alluvium : Thames. 



Absolute. Reductions. 



18-7 

 13-7- 

 8-6 

 8-6 

 9-0 

 50 



57 



10-5 



5-2 

 4-8 



4-0 

 11-0 



100 217 



73-4 159 



46 100 

 46 100 



48-2 1 105 



26-8 I 58-2 



30-5 I 60-2 



5G-2 122 



GO-5 

 55-9 



46-5 

 128 



From this description it is clear that the fossil navicuhir 

 heioiiged to an animal possessing close affinities with the 

 Vj aver; nevertheless, the differences observed are of generic 

 importance. A comparison of the articulations shows that 

 the fossil formed part of a considerably larger foot than that 

 of Castor. The only larger beaver-like rodent known from 

 the Forest Bed is the Trocjontherium, and, in view of all the 

 facts, no reasonable doubt can remain that the fossil is rightly 

 referred to this genus. In the l)eaver the fourth metatarsal 

 is the longest and stoutest, the third is little shorter though 

 more slender, the second and fifth are much smaller, and tiiat 

 of the hallux is still further reduced. From iho fact that the 

 facette for cuneiform 111. is narrower, while tiiose for 

 cuneiforms II. ami I. are wider and more ext Misivcdy developed 

 in the fossil, we may infer that the disparity in the size of 

 the three cuneiforms, and consequently of the first, second, 

 a!i 1 third metatarsals which they support, was less marked 

 ill the Trogontherium than in the ijeaver. The slighter 

 development of the posterior spur in the fossil betokens less 

 powei fully d:\ eloped fh'xor muscles. The enlargement ot 



