[Illustration: From Owen.
FIG. 14.--Lower Jaw and Teeth of _Phascolotherium bucklandi_ (nat.
size in outline).]
[Illustration: From Owen.
FIG. 15.--Spalacotherium tricuspidens (twice nat. size), Purbeck
beds.]
Of the Old World forms, the family _Triconodontidae_ is typified by
the genus _Triconodon_, from the English Purbeck, in which the
cheek-teeth carry three cutting cusps arranged longitudinally. There
seems to have been a replacement of some of these teeth; and it has
been suggested that this was of the marsupial type. To the same family
are referred _Phascolotherium_ (fig. 14), of the Lower Jurassic
Stonesfield slate of England, and _Spalacotherium_ (fig. 15), of the
Dorsetshire Purbeck; the latter having the three cusps of the
cheek-teeth rotated so as to assume a tritubercular type. Other genera
are _Menacodon_ and _Priacodon_, the former American, and the latter
common to Europe and North America. By one authority _Amphilestes_
(fig. 16), of the Stonesfield Slate, is included in the same group,
while by a second it is regarded as representing a family by itself.
_Amphitherium_, of the Stonesfield Slate, typifies the family
_Amphitheriidae_, which includes the American _Dryolestes_, and in
which some would class the European Purbeck genus _Amblotherium_,
although Professor H. F. Osborn has made the last the type of a
distinct family. Yet another family, according to the palaeontologist
last named, is typified by the genus _Stylacodon_, of the English
Purbeck. To mention the other forms which have received names will be
unnecessary on this occasion.
[Illustration: From Owen.
FIG. 16.--Lower Jaw and Teeth of _Amphilestes broderipi_ (twice nat.
size).]
It will be observed from the figures of the lower jaws, which are in
most cases the only parts known, that in many instances the number of
cheek-teeth exceeds that found in modern marsupials except
_Myrmecobius_. The latter has indeed been regarded as the direct
descendant of these Mesozoic forms; but as already stated, in the
opinion of Mr B. A. Bensley, this is incorrect. It may be added that
the division of these teeth into premolars and molars in figs. 14 and
16 is based upon the view of Sir R. Owen, and is not altogether
trustworthy, while the restoration of some of the missing teeth is
more or less conjectural. As regards the affinities of the creatures
to which these jaws belonged, Professor Osborn has referred the
_Triconodontidae_ and _Amphitheriidae_, together with the
Curtodontidae (as represented by the English Purbeck _Curtodon_), to a
primitive group of marsupials, while he has assigned the
_Amblotheriidae_ and _Stylacodontidae_ to an ancestral assemblage of
Insectivora. On the other hand, in the opinion of Professor H. Winge,
a large number of these creatures are primitive monotremes. Besides
the above, in the Trias of North America we have _Dromotherium_ and
_Microconodon_, extremely primitive forms, representing the family
_Dromotheriidae_, and apparently showing decided traces of reptilian
affinity. It may be added that a few traces of mammals have been
obtained from the English Wealden, among which an incisor tooth
foreshadows the rodent type.
AUTHORITIES.--The above article is partly based on that by Sir W. H.
Flower in the 9th edition of this work. See also O. Thomas, Catalogue
of Monotremata and Marsupialia in the British Museum (1888); "On
_Caenolestes_, a Survivor of the _Epanorthidae," Proc. Zool. Soc.
London_ (1895); J. D. Ogilby, Catalogue of Australian Mammals (Sydney,
1895); B. A. Bensley, "A Theory of the Origin and Evolution of the
Australian Marsupialia," _American Naturalist_ (1901); "On the
Evolution of the Australian Marsupialia, &c.," _Trans. Linn. Soc._
(vol. ix., 1903); L. Dollo, "Arboreal Ancestry of Marsupials,"
_Miscell. Biologiques_ (Paris, 1899); B. Spencer, "Mammalia of the
Horn Expedition" (1896); "Wynyardia, a Fossil Marsupial from
Tasmania," _Proc. Zool. Soc. London_ (1900); J. P. Hill,
"Contributions to the Morphology of the Female Urino-genital Organs in
Marsupialia," _Proc. Linn. Soc. N. S. Wales_, vols. xxiv. and xxv.;
"Contributions to the Embryology of the Marsupialia," _Quart. Journ.
Micr. Science_, vol. xliii.; E. C. Stirling, "On _Notoryctes
typhlops_," _Proc. Zool. Soc. London_ (1891); "Fossil Remains of Lake
Cadibona," Part I. _Diprotodon, Mem. R. Soc. S. Australia_ (vol. i.,
1889); R. Broom, "On the Affinities of _Thylacoleo," Proc. Linn. Soc.
N. S. Wales_ (1898); H. F. Osborn, "Mesozoic Mammalia," _Journ. Acad.
Nat. Sci. Philadelphia_ (vol. ix., 1888); E. S. Goodrich, "On the
Fossil Mammalia from the Stonesfield Slate," _Quart. Journ. Micr.
Science_ (vol. xxxv., 1894). (R. L.*)