360 H. LydeJil-er — On EstJionyx and Platychcerops. 



v. — Note on the Generic Identity of the Genus E'^thovyx, 

 Cope, WITH Flattchcerops, Charlesworth {=iMiolophus, Owen). 



By R. Lydekker, B.A., F.G.S., etc. 



IN an early number of tbe present serial ^ Prof. Sir E. Owen de- 

 scribed and figured the hinder part of the palate of a small 

 mammal from the London Clay of Heme Bay,^ under the new name 

 of Miolophus planiceps. The specimen is now preserved in the 

 Museum at York, and had been previously described by Mr. E. 

 Charlesworth ^ under the name of Platychcerops Bichardsoni ; a cir- 

 cumstance which seems to have escaped the notice of Sir R. Owen. 

 This name having the priority should supersede that of Miolophus.^ 

 The specimen (of which there is a cast in the British Museum) 

 shows the second and third true molars of both sides, and on the 

 right side the fourth premolar and the alveoli of pm 3 and m. 1. Both 

 the later premolars and true molars are of the same general form, 

 and have tri tubercular crowns. Sir R. Owen regarded the specimen 

 as indicating a form allied to Hyracotherium (including Fliolophus) ; 

 but the similarity between the premolars and true molars and the 

 trituberculate crowns of the latter forbids the acceptance of this view. 



In 1874 Prof. Cope ^ founded a new genus, from the reputed Eocene 

 of New Mexico, under the name of Esthonyx, the type species being- 

 named E. Burmeisteri. In two subsequent communications ^ the same 

 writer determined the dental formula of this form to be I. f, C. i, 

 Pm. f , M. f ; and in the latter of the two he gives a reduced figure 

 of the right half of the palate.'' The third (penultimate) premolar 

 has one external and one internal cusp, and is separated by a distinct 

 interval from the teeth on either side. In the fourth premolar these 

 cusps are much enlarged, and the tooth is transversely elongated. 

 The true molars have two external cusps, which are flattened, close 

 together, and well within the margin of the base of the crown. 

 There is one internal cusp, and a strong posterior ledge. 



This description applies word for word to the palate o^ Platychcerops 

 Bichardsoni ; and if the figure of the latter be compared with that of 

 the so-called Esthonyx Burmeisteri, the close resemblance of the two 

 will be self-evident. The European form exhibits the isolation 

 of the alveolus of pm 3, and the marked contraction of the cranium 

 at the level of this tooth. 



The writer has, therefore, no hesitation in uniting Esthonyx with 

 Platychcerops. The American P. Burmeisteri appears to have been 



1 Geol. Mag. Dec. I. Vol. II. p. 339, PI. X. Fig. 1 (1865). 



^ Erroneously stated to be from Sheppey. 



^ Rep. Brit. Assoc, for 1854, Trans, of Sections, p. 80. See also Geol. Mag. 

 Dec. I. Vol. III. p. 48 (1866). 



* The description is somewhat vague, and the two sides of the molars are reversed 

 in the description, 



5 Rep. U.S. Geogr. Surv. W. of 100th Meridian, Vert. Foss. New Mexico, p. 6 

 (1874), 8vo. 



6 Proc. Amer. Phil. Soc. 1831, pp. 147-148 ; and Amer. Nat. 1884, pp. 479-480. 

 ■^ A full-sized figure is given in Rep. U. S. Geol. Suit. vol. iii. pi. xxiv. C. fig;. 1 



(1884). 4to. 



I 



