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Bibliographical Notices. 275 
fifteen fossil species, according to Mr. Lydekker’s table, all occur in 
the Miocene rocks of Europe and North America. Some contribu- 
tion is made to the knowledge of Acerotherium in the description of 
a cranium, of which the author gives a restoration. As compared 
with the Acerotherium incisivum, the Indian species has the nasal 
bones thicker at the base and apparently shorter ; there is a greater 
depth from the dental border of the orbit to the teeth ; the temporal 
fossee in the Indian form are wider and shorter, and other differences 
help to distinguish the species. The dentition is described in detail, 
from which it appears that there are four premolar teeth and three true 
molars, while in front of the premolars there is the root of an incisor. 
These teeth are characterized by a well-marked cingulum, which 
distinguishes this animal from the associated species of rhinoceros, 
Fough the angulum is well developed in the Rhinoceros deccanensis 
of Foote. 
Having compared the dentition with such types as were likely to 
throw light upon the species, the author passes on to the genus 
Rhinoceros, recognizing thirty species living and fossil, of which 
the four Siwalik species defined by Dr. Falconer still remain the 
only Indian types from this horizon. The author commences with 
some notice of the Rhinoceros sivalensis, affirming that the species 
is not hexaprotodont, describes some molar teeth, and points 
out resemblances between the molars of this species and those of 
Rhinoceros javanicus, and observes that the only character by which 
he can distinguish the molars of the living and fossil form is a diffe- 
rence in the relative dimensions of the teeth—the greatest width 
of the anterior surface being exactly equal to the greatest length of 
the external surface in the molars of R. sivalensis, whereas in R. 
javanicus the anterior measurement is greater than the external 
-measurement ; so that, were it not for the difference in form of the 
skull, the author doubts whether a specific difference could be esta- 
blished on the character of the teeth. This tooth-character is of 
some interest, since Acerotherium and all the Miocene species of 
Rhinoceros possess teeth of the type represented at the present day 
by the rhinoceros of Sumatra, which approximates towards the teeth 
of Paleotherium, Anchitherium, Hyachyus, and other old Perisso- 
dactyles ; and on this circumstance Mr. Lydekker relies in explain- 
ing the resemblance between the milk-molars of the Sumatran and 
Indian types, because ancestral characters are often retained in the 
deciduous teeth long after they are lost in the permanent teeth. 
Hence he refers all species which approximate to the Rhinoceros 
indicus to a comparatively recent origin, the oldest form, Rhinoceros 
platyrhinus, only occurring in such parts of the Siwalik beds as are 
of Pliocene age. An excellent critical discussion of the mandible 
results in the conclusion that the form hitherto referred to Rhino- 
ceros paleindicus must be assigned to the Rhinoceros sivalensis, 
partly because there is no known unicorn species without lower in- 
cisors, and partly because the platyrhine type of jaw is found in 
the beds which yield the molars of Rhinoceros sivalensis, but also 
because in form the jaw and teeth so closely resemble “ the corre- 
