1867.] BOYD DAWXINS RHIIfOCEROS LEPTOEHINTJS. 219 



the anterior (m) bears two costce (hi & h 2), faintly divided from 

 each other by a broad shallow Y-shaped depression, while the jpos- 

 terior (n), tumid basally, is sloped off abruptly from the base 

 towards the crown-summit. The presence of the costce defines the 

 tooth from the megarhine homologue, the tumidity of the posterior 

 area (n) from the tichorhine. On the crown-surface the anterior 

 valley (a) is more shallow than the posterior (b) ; and of the three 

 colles, as in all the homologous teeth of the genus, the median (e) is 

 the largest. The summit of the latter is flattened antero-posteriorly 

 at its inner side ; and the transverse bridge of enamel that joins it from 

 the external lamina is traversed by a notch ending in a cleft. The 

 result of this arrangement would be, that in the slightly worn tooth 

 the summit of the median collis (e) would exhibit a trefoil pattern, 

 somewhat after the fashion of the teeth of the Pig and Hippopota- 

 mus. The low crown, the smoothness of the enamel, and the small 

 size differentiate the tooth from the corresponding one of the ticho- 

 rhine species, while the latter characteristic affords an easy means of 

 defining it from the closely allied megarhine form. 



4. Permanent Upper Dentition. — The entire permanent series of 

 the teeth of this species was obtained by the late Mr. John Brown, of 

 Stanway, from the brickfields of Lexdeu, near Colchester, in associa- 

 tion with remains oi Hippopotamus major and jjjlep>has antiquus, and 

 are preserved in the British Museum. The upper-jaw teeth very 

 closely resemble those of the megarhine Rhinoceros, but are distin- 

 guished from them by the possession of the following characteristics : 

 — by the rugosity of the enamel surface, by the development of a third 

 costa (Jc 3) on the posterior area of premolars 3 and 4, by the con- 

 cavity of the base of the external lamina (I), and by the inner side 

 of the collis not being sloped off so abruptly as in the former species. 

 As compared with the tichorhine Ehinoceros, the absence of the 

 anterior combing-plate (g), so persistent in the teeth of that animal, 

 the height of the entrance of the anterior valley in Premolars 3 and 

 4, the comparative smoothness and thinness of the enamel, the 

 faintness of the costce on the external lamina, the gradual slope of 

 the collis on the inner side, and the great development of the guard, 

 or stout ascending ridge of enamel on the anterior surface, are the 

 salient points upon which a specific determination can be made. 

 Besides these, also, the most noteworthy in the jaw under considera- 

 tion are the stoutness of the guard in premolars 3 and 4, and the 

 passage of a ridge across the entrance of their anterior valley 

 (a). The posterior wall, also, or third collis bears a cusp, as in 

 the tichorhine species ; but it is faintly developed and is soon worn 

 away. 



Pigures 3 and 4 (PI. X.), which I owe to the kindness of my friend 

 Professor Phillips, P.E.S., of a right upper premolar 4, from the 

 Crawley Eocks, near Swansea, show all the salient points of the 

 Upper premolar dentition of the species ; while fig. 5, of a second 

 upper true molar from Peckham, is typical of the leptorhine upper 

 true molars. We are indebted to Professor Owen for a figure of 

 the leptorhine first upper tru.e molar from Clacton, in ' British Fossil 



VOL. XXIII. PART I. R 



