TKOGONTHERIUM CUVIERI. 187 



Cromer. The stratum of clay is eight feet thick, and con- 

 tains pyrites : its upper part is at about high water-mark, 

 and it forms the beach. Here, or in situ in the blue clay, 

 were discovered bones of the Mammoth, Rhinoceros, Ox, 

 Horse, and Deer. 



The Trogontherian relic is a portion of the right ramus of 

 the lower jaw, containing half the root of the great in- 

 cisor, and the three anterior molar teeth in situ. The 

 proportions of these teeth differ conspicuously from those 

 in the Beavers, both European and American. The an- 

 tero-posterior and transverse diameters of the first grinder 

 exceed by one-third those of the second grinder : both 

 the second and third molars are smaller in proportion to 

 the incisor than in the Beaver ; and the socket of the 

 fourth tooth shews this to have had a longer antero- poste- 

 rior diameter than the third grinder, which is the reverse 

 of the proportions of these teeth in the genus Castor. The 

 grinding surface of the first molar, m, which alone bears the 

 same proportion to the incisor as in the Beaver, has the 

 same number and general direction of enamel-folds, viz. 

 four, three continued from the inner side of the tooth, 

 and one from the outer side, and this extends further into 

 the substance of the tooth than in the Beaver, at an age 

 when the molars are as much worn down as in the present 

 specimen. The two succeeding grinders of the TrogontJie- 

 rium differ in a more marked degree from the correspond- 

 ing teeth in the genus Castor, having but two inflected 

 folds of enamel, one from the outer, the other from the 

 inner side of the tooth ; the latter also being relatively 

 longer than the single inner fold of enamel in the Beaver's 

 grinders, all of which retain the three outer folds of enamel. 



The opportunity of instituting these comparisons is the 

 more valuable, since M. Fischer has not entered into the 



