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Show 248 MR. E. T. NEWTON ON TROGONTHERIUM CUVIERI. [Apr. 21, cuvieri from the Forest-bed of East Runton, near Cromer, of which the following is an abstract:- In the year 1846 Sir Richard Owen referred certain Beaver-like jaws and teeth from the Cromer Forest-bed to the Trogontherium cuvieri of Fischer, and although some doubt was thrown upon this reference he maintained the correctness of his determination in 1869, when describing some further remains of this rodent. The type of Fischer's Trogontherium being a skull, it was very desirable that a similar specimen should be found in the Forest-bed, which could be compared with it; but hitherto the only parts of skulls which have come to hand have been mere fragments. Recently, however, Mr. A. Savin, of Cromer, has obtained a nearly perfect skull from East Runton, and it is this which is fully described in the present communication. A comparison with the skull of a Beaver (Castor) shows that although in a general way resembling it, yet the differences are certainly of generic importance. One of the chief points of difference is found in the structure of the cheekteeth ; for while in the Beaver the enamel-folds are open to the exterior of the teeth down to their bases, in the Trogontherium they are open for only a short distance from the summit, and consequently with wear they are soon separated from the exterior and form islands of enamel, some of which may become obliterated at a comparatively early stage. It follows from this that well-worn teeth may have fewer enamel-folds than others in an earlier stage of wearing, a fact which has led to errors in the determination of the affinities of this fossil rodent. When compared with the type skull of Trogontherium, this Forest-bed specimen is found to agree so closely with it in form and structure, as well as in the arrangement of the enamel-folds of the teeth, as to leave little doubt as to their specific identity. And a further comparison with the Conodontes boisvilleltii of Laugel, from the Pliocene of Saint Prest, reveals no difference of specific value. The study of this new specimen from the Cromer Forest-bed thus confirms Sir Richard Owen's reference of these English and French rodents to the Trogontherium cuvieri of Fischer. This memoir will be published entire in the Society's 'Transactions.' The following papers were read :- |