ON DITROTODON MINOR, HUX. 



41 



in another species is not a mere assumption. But, fortunately, we 

 are able to show that such intermediate condition is also exemplified 

 in a Diprotodon corresponding in size to D. minor. In a maxilla, 

 wanting only the last molar, and about a fourth smaller in every 

 part than 1). australis the premolar has the mesial indent, and that 

 alone, fashioned as in D. minor (type), the rest of the outer surface 

 being very much as in Sir R. Owen's figure of N. mitchelli (PI. 88, 

 fig. 11, E.M. of Aust.), and consequently it shows neither the three 

 vertical ridges of the one type (minor), nor the merely undulating 

 surface of the other (australis ?). Unless then, we are prepared to 

 accept this tooth also as the index of a distinct species (and the 

 presence of at least four different Diprotodons on a few square 

 miles of old Australia is improbable), we must take the alternative 

 and conclude that the premolar of D. minor had externally a range 

 of variation of perhaps tin usual extent from the comparatively 

 angular to the comparatively smooth condition; An 1 symptoms of 

 its variability are not shown by its outer surface only. The prebasa* 

 tuberde which, according to the figures, is much less developed in 

 the type specimen of D. minor than in its co-type (D. australis ?) is 

 in the example before us, intermediate in size, and differs from both 

 in its close approximation to the lobe behind it — an approximation 

 apparently due to the contraction of the prebasal talon which 

 renders the whole tooth about 3 mm. shorter than the typp, which 

 again is shorter than the co-type. Professor Huxley ment : ons a 

 difference in the form of the antero-internal ridges, and it may be 

 gathered from the figures that this consists in the prolongation of 

 the ridge in D. minor, so far backwards as to render it confluent 

 with the postero-internal ridge ; whereas in the companion tooth it 

 terminals as in D. australis, on the tore-angle of the lobe — in this 

 respect the example of D. minor in hand agrees with D. (australis ?). 

 In all the specimens of D. minor the dentinal band is much con- 

 tracted in width as, in its anterior course, it approaches the inner 

 side of the tooth ; the antero-external portion of the unworn summit 

 was therefore, in this species, more or less divided off from the rest 

 by an anterior and posterior indent ; but there is no indication of 

 apical separation of the postero-external from the postero-internal 

 part of the cusp. We are consequently, unable to see in it a tooth 

 composed of external and internal lobes, much less of large external 



