■26 FOSSIL MAMMALIA OF THE 



Beckles, Esq., F.R.S., and the success of his explorations, carried on at much cost and 

 personal risk, may be estimated by what follows of the present Monograph, the subjects of 

 which were exclusively brought to light by Mr. Beckles, 



I commence with those which tend to complete our knowledge of the mandible and 

 mandibular dentition of Bpalacotlierium. 



PI. I, fig. 35, represents, of the natural size, in outline, and magnified three times, 

 in tint, at a, the fore part of the left mandibular ramus, showing its outer side, and 

 an impression of the hinder part to near the beginning of the rising branch of the same 

 jaw. The horizontal ramus is vertically narrow, but is thick, being convex outwardly ; 

 it is flatter on the inner side, the impression of which shows a trace of the longitudinal 

 groove {g). The ramus gradually contracts, with a gentle inferior convex curve, to the fore 

 end, which is not abruptly raised, or bevelled up. There are four rather close-set simple 

 alveoli, anterior to the three premolars, with more or less mutilated crowns, in place. The 

 fourth alveolus is that of the canine (c). The second premolar (2) shows, as in fig. 34, the 

 main cone less raised in proportion to its breadth than in the succeeding teeth. The tip 

 of the higher cone of the third premolar (3) is preserved, with the impression of the two inner 

 basal cusps. The fourth and fifth of the molar series are not preserved. The sixth and 

 seventh are shown by impressions of the two inner cusps (see fig. 34b, e, s). Impres- 

 sions of the two or three following teeth are less recognisably preserved. There is a small 

 outlet of the dental canal beneath the first premolar, and a second beneath the alveolus of 

 the third or last incisor {i 3). 



Figures 36 and 37 show the portions and impressions of a mandibular ramus with 

 teeth of Spalacotherium tricuspidens preserved in counterpart slabs of a split block of 

 Purbeck shale. 



In fig. 36, a portion of the middle of the horizontal ramus exposes its inner surface, 

 and includes three teeth (3, 4, 5) more or less mutilated, with part of a fourth (6). In 

 fig. 37 the continuous hinder part of the ramus is preserved, showing the outer surface, 

 and includes the basal half of the crown of the sixth and seventh molars, with indications 

 of the sockets of the eighth and ninth molars. The tenth molar (lo) is in part preserved, 

 together with the hind part of the ramus, broken off, and somewhat displaced, showing 

 the characteristic contraction preceding the expanse into the ascending branch with the 

 crotaphyte fossa. 



The impression anterior to the portion of jaw preserved in this block answers to the 

 part of the ramus preserved in the counterpart block : in advance of which impression a 

 small portion of the fore part of the ramus remains, showing the posterior outlet beneath 

 the socket of the first premolar. 



The teeth retained in the block (fig. 36) are the third, fourth and fifth of the molary 

 series. Anterior to them is the impression of the second, showing the same proportions of 

 the main-cone as in 2, fig. 34. That of the third premolar (3) in fig. 36 wants the apex. 



