Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/647

1870.] BUSK RHINOCEROS OF ORESTON. 465 5. In the direction of the crista, which, when present in R. hemitoechus, arises further back from the outer lamina, or even from the base of the hinder column itself, and projects in a direction nearly parallel with the uncus, instead of at right angles to it.

2. Other Bones.

Most of the bones, as I have said, are in a very fragmentary condition; but amongst them are one or two which are capable of affording excellent characters, and are, in fact, alone sufficient, as it seems to me, to determine the species to which they belong.

The first of these is a right middle metacarpal, (no. 905 in the Catalogue). The bone is nearly perfect ; and its growth is completed, inasmuch as no trace remains of the junction between the shaft and the epiphysis.

Regarded with respect either to its size or to its form and proportions, this bone differs so strikingly at first sight from the corresponding bone in any other species of Rhinoceros, recent or extinct, with which I am acquainted, that it is surprising its true specific relations should have been so long overlooked. First, as regards its size. In Table I. (in which the dimensions and proportions of the middle metacarpal, in several instances, of R. leptorhinus and R. tichorhinus are given), it will be seen that the Oreston bone is nearly 1-1/2 inch longer than the longest specimen of R. tichorhinus of which I have any knowledge, and, in the second place, that it nearly corresponds in length with the metacarpal of R. leptorhinus, as shown in two specimens from Grays Thurrock, in the British Museum*. As regards the other dimensions, it will also be seen considerably to exceed those of R. tichorhinus — as, for instance, in the size of the two extremities, and especially in the transverse diameter of the distal articular surface or trochlea, which may be regarded as affording a pretty certain term of comparison. With respect to the least circumference of the shaft, it is true that in one instance of Rhinoceros tichorhinus that has come under my observation, from the river-gravel at Stratford-on-Avon, the cir-

hemitoechus from R. leptorhinus ; and, in the main, I think he was quite right in so doing. But it must not, so far as I can judge, he supposed that this character affords an invariable criterion in all cases. Several instances, besides the present, showing this, may be cited from the figures given in the ' Palaeontographical Memoirs ' and elsewhere. For instance, in the lower jaw from Lyons, of which a figure is given in pl. xxxi. fig. 2, the crochet appears to rise very much in the same way as in the Oreston teeth, that is to say, at an acute angle, and then to curve outwards. Again, in Mr. B. Dawkins's fig. 10 (N. Hist. Rev. v. p. 410), the crochet cannot be said to arise at an open angle, but the reverse ; and the same may be said of the milk-molar, fig. 4 (l. c. p. 405). I have also in my possession a mm 3 from Ilford, belonging to Mr. Prestwich, in which the same may be observed ; and, further, from this specimen it is apparent that as the tooth wore down, the angle would become more and more open ; so that, without throwing any doubt upon the general usefulness of the form of the angle as a diagnostic character, it is, I think, one which requires to be used with caution.

improbable they may be the right and left of the same individual.
 * From the close similarity of these two metacarpals from Grays, it is not