1857.] OWEN PLIOLOPHUS VULPICEPS. 65 



ing "two transverse eminences connected by a diagonal crest* ;" and 

 such is described as the type of the lower true molar teeth in Lo- 

 phiotherium f and Tapirulus%. This is, in fact, the structure of 

 the lower molar teeth in Lophiodon proper, and that by which it 

 so nearly resembles the existing Tapirs. 



Pliolophus differs from all previously known Lophiodonts by the 

 division of the part of the tooth answering to the " colline trans- 

 verse " into two distinct cones, PI. III. fig. 6, a, b and c, d ; and the 

 penultimate molar, m 2, more especially differs from that tooth in all 

 hitherto known eocene or later forms of hoofed Mammals, in having 

 a third cone, e, interposed between the two anterior cones, and thus 

 exhibiting three cones on the same transverse line, as in the upper 

 molars ; — a structure which we have hitherto seen only in the small 

 mammal of the Lower Oolite described under the name of Stereo- 

 gnathus ooliticus §. I expressed my regret, at that period, when I 

 could only cite the upper molars of Hyracotherium and of a few other 

 eocene Ungulates as manifesting the three transverse cones, that the 

 structure of the lower molars in Hyracotherium was then unknown. 

 As the Pliolophus, though in some respects intermediate between 

 the Lophiodon and Hyracotherium, has a closer affinity to the latter, 

 we may, with some confidence, regard the modifications of its lower 

 molars as significant of those that the same teeth of Hyracotherium 

 will present when found. And the unlooked-for confirmation of 

 my expectation of some further illustration of the affinities of Stereo- 

 gnathus by the lower molars of Hyracotherium, through the now 

 acquired knowledge of the structure of those in the nearly allied 

 Pliolophus, adds, in the same degree, probability to the inference 

 which was founded upon the resemblance between the lower molars 

 of Stereognathus and the upper ones of Hyracotherium. In offer- 

 ing this remark, however, I am quite sensible how uncertain any in- 

 ference from a single lower molar is shown to be by the degree of 

 resemblance in the structure of the lower molar teeth which exists in 

 Tapirus, Macropus, Lophiodon, Dinotherium, and Manatus, and, 

 again, in those of Hippopotamus and Halitherium. The reference 

 by Cuvier of detached teeth of the Halitherium to the genus Hippo- 

 potamus, and of detached teeth of Dinotherium to the genus Tapirus, 

 just and exact as were these references, viewed as expressions of the 

 correspondence detected by a comparison of the fossil with the recent 

 teeth, ought to warn us against placing too much confidence in den- 

 tal characters, exclusively, as proofs of the closer degrees of deter- 

 mination which Cuvier has shown must depend upon an empirical 

 study of coincidences, rather than on the rational deductions from 

 correlations. 



The same caution I now feel to be instructively reiterated by my 

 reference of the Hyracotherium, on the ground of similarity of modi- 



* " A deux collines transverses reliees par une crete en diagonale." Paleonto* 

 logie Francaise, descr. of pi. 17. 



t Ibid. pi. 11. f. 10-12. + Ibid. pi. 24. 



§ Quart. Journ. Geol. Soc. vol. xiii. Part I. February 1857, pp. 1, &c. pi. L 

 VOL. XIV. — PART I. F 



