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. brongniarti. 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 premaxille of the present form were 
cing aborted. The dimensions of the present form are as 
ollows :— 
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 
BISCLUOGH, , o'er runes Sh eee ee 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,I can 
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 Platyonyex 
ought to be merged.in Scelidotherium. 
Platyonyz 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 brong- 
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 differences 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, 8. 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. drongniarti) 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 
* Monatsb. k. preuss. Ak. Wiss, 1881, pp. 374-380. 
* ‘Mammiféres fossiles de l’ Amérique méridionale,’ p. 151 (1880). 
* Memoir on the Mylodon, p. 170, note. 
Proc. Zoou. Soc.—1886, No. XXXIII. 33 
