258 APPENDIX. 



their osteological characters to such an extent as to leave no 

 doubt as to the correct determination of their true affinities. 



It is much to be regretted, however, that many of these 

 animals have received different names from different authors, a 

 fact specially conducive to confusion in the nomenclature of the 

 science. It appears that the only way to obviate this difficulty 

 is by strict adherence to priority in the employment of a name, 

 provided it is accompanied by a competent description, and the 

 use of such characters as will distinguish the animal named 

 from its nearest allies. If unaccompanied by these differential 

 characters, it is a nomen nudum, and can have no claim what- 

 ever to rank with those that have been properly defined. I 

 mention these facts with the hope of establishing a criterion by 

 which to judge which name it is proper to retain and which it 

 is proper to discard ; and, to elucidate the subject, I will gives 

 the names of a few animals that have been discovered during 

 the past forty years. 



In 1841 Prof. Richard Owen described the remains of a 

 Lophiodon-like* animal, from the London clay of Eocene age, 

 to which he gave the name Hyracotherium.] Subsequently he 

 described a nearly allied genus, from the same deposit, under 

 the name Pliolophus.^ In Hyracothcrium the molar and pre- 

 molar teeth are different, both above and below. In Pliolophus 

 the last, or fourth inferior premolar, is like the first true molar, 

 a character which separates the two genera satisfactorily. The 

 specimens described by Prof. Owen do not display clearly the 

 number of digits either possessed, but he expresses the opinion 

 that Pliolophiis has three toes on the posterior limbs. 



* The Lophiodons were first described by Cuvier. They were allied to 

 the tapir. They derive their name from the structure of the true molars, 

 which have their crowns crossed transversely by two crests or ridges of 

 dentine, covered with a layer of enamel. The last lower molar has also a 

 email posterior lobe. The premolars are more simple in structure and 

 compressed, resembling the first premolars of the tapir. The upper molars 

 also resemble those of the tapir, but approach in some respects those of 

 the rhinoceros. The diastema, or toothless interval between the canine 

 and premolar teeth, was much shorter than in the tapir. Several species 

 have been described from the Eocene of France and England, but little is 

 known of the skull or skeleton. No true Lophiodon is yet certainly known 

 in this country. 0. C. Marsh. 



t Transactions London Geological Society, 1841, pp. 203-208. 



J Loc. Cit, pp. 54-72, 1858. 



