1886.] MR. R. LYDEKKER ON SCELIDOTHERIUM. 497 



the nasals themselves are more pointed posteriorly and wider 

 anteriorly, the width of the anterior expansion being greater than 

 that at the frontal expansion, while the reverse condition obtains in 

 S. brongnim'ti. The resemblance between the two crania is, how- 

 ever, sufficiently close to render it probable that the two forms were 

 closely allied, and that the premaxillse of the present form were 

 similarly aborted. The dimensions of the present form are as 

 follows : — 



Length of the facial portion of maxilla 0"122 



Width of the two occipital condyles 0*099 



Length from condyles to last tooth 0'238 



Length of upper dental series 0"093 



Length of mandibular symphysis 0*124 



Interval between hinder border of symphysis and 



first tooth 0-012 



Since the present form is decidedly distinct from all the species 

 mentioned above, and since I cannot identify it with either of the 

 other ill-defined forms referred to Scelidotherium and Platyonyx,! c&n 

 only adopt the course followed in the case of the preceding species ; 

 and I accordingly propose to designate this form as Scelidotherium 

 chiliense, since I shall immediately show that the genus Platyonyx 

 ought to be merged in Scelidotherium. 



Platyonyx is stated by Lund (and his view is followed by Dr. 

 Burmeister') to be distinguished from Scelidotherium by the absence 

 of an entepicondylar foramen to the humerus, and by the more 

 flattened phalangeals; while, according to Messrs. H. Gervais and 

 Ameghino^, the crochet of the last lower tooth is more prominent. 

 Sir R. Owen '\ who unites the two genera, is of opinion that the 

 limb-bones referred by Lund to Platyonyx really belong to Glyptodon. 

 I have no means of deciding which of these two views is correct ; 

 but the close general resemblance in the structure of the nasals of 

 Scelidotherium chiliense to those of the so-called Platyonyx hrong- 

 niarti leads me to conclude that whether the humerus of the latter 

 was, or was not, provided with an entepicondylar foramen, the species 

 is not entitled to generic distinction from Scelidotherium, the 

 alleged difl'erences in the structure of the phalangeals and of the last 

 lower tooth being characters which are certainly not more than 

 specific ones. 



Taking the three species, S. leptocephalum, S. bravardi, and S. 

 chiliense together, it will be seen that they form a sequence as 

 here placed in regard to the length of the nasals — S. chiliense 

 (together with S. bi-ongniarti) being the least, and S. leptocephalum 

 the most removed from the type of cranium obtaining in Mega- 

 therium. 



Affinities of the Genus. 



In conclusion, I may observe that Scelidotherium appears to be a 



1 Monatsb. k. preuss. Ak. Wiss. 1881, pp. 374-380. 

 ^ ' Mammiferes fossiles de I'Amerique meridionale,' p. 151 (1880). 

 ^ Memoir on the Mylodon, p. 170, note. 

 Proc. Zool. Soc— 1886, No. XXXTII. 33 



