ralia than with any other living form.
If this conjecture be correct, these ancient Mammals belonged to
the order of the Marsupials or Pouched Quadrupeds (_Marsupialia_),
which are now exclusively confined to the Australian province,
South America, and the southern portion of North America. In the
Old World, the only known Triassic Mammals belong to the genus
_Microlestes_, and to the probably identical _Hypsiprymnopsis_ of
Professor Boyd Dawkins. The teeth of _Microlestes_ (fig. 157)
were originally discovered by Plieninger in 1847 in the "bone-bed"
which is characteristic of the summit of the Rhaetic series both
in Britain and on the continent of Europe; and the known remains
indicate two species. In Britain, teeth of _Microlestes_ have been
discovered by Mr Charles Moore in deposits of Upper Triassic age,
filling a fissure in the Carboniferous limestone near Frome, in
Somersetshire; and a molar tooth of _Hypsiprymnopsis_ was found
by Professor Boyd Dawkins in Rhaetic marls below the "bone-bed" at
Watchet, also in Somersetshire. In North America, lastly, there
has been found in strata of Triassic age one of the branches
of the lower jaw of a small Mammal, which has been described
under the name of _Dromatherium sylvestre_ (fig. 156). The fossil
exhibits ten small molars placed side by side, one canine, and
three incisors, separated by small intervals, and it indicates
a small insectivorous animal, probably most nearly related to
the existing _Myrmecobius_.

LITERATURE.

The following list comprises a few of the more important sources of
information as to the Triassic strata and their fossil contents:--

(1) 'Geology of Oxford and the Valley of the Thames.' Phillips.
(2) 'Memoirs of the Geological Survey of Great Britain and Ireland.'
(3) 'Report on the Geology of Londonderry,' &c. Portlock.
(4) "On the Zone of Avicula contorta," &c.--'Quart. Journ. Geol.
Soc.,' vol. xvi., 1860. Dr Thomas Wright.
(5) "On the Zones of the Lower Lias and the Avicula contorta
Zone"--'Quart. Journ. Geol. Soc.,' vol. xvii., 1861. Charles
Moore.
(6) "On Abnormal Conditions of Secondary Deposits," &c.--'Quart.
Journ. Geol. Soc.,' vol. xxiii., 1876-77. Charles Moore.
(7) 'Geognostische Beschreibung des Bayerischen Alpengebirges.'
Guembel.
(8) 'Lethaea Rossica.' Pander.
(9) 'Lethaea Geognostica.' Bronn.
(10) 'Petrefacta Germaniae.' Goldfuss.
(11) 'Petrefaktenkunde.' Quenstedt.
(12) 'Monograph of the