THE JURASSIC PERIOD. 253. 
able peculiarities of its structure from all existing members of 
the class of Birds. This extraordinary Bird (fig. 182) appears 
to have been about as big as a Rook—the tail being long and 
extremely slender, and composed of separate vertebree, each 
of which supports a single pair of quill-feathers. In the flying 
Birds of the present day, as before mentioned, the terminal 
vertebre of the tail are amalgamated to form a single bone 
(“‘ ploughshare-bone ”), which supports a cluster of tail-feathers ; 
and the tail itself is short. In the embryos of existing Birds 
the tail is long, and is made up of separate vertebrz, and the 
same character is observed in many existing Reptiles. The 
tail of Archaeopteryx, therefore, is to be regarded as the per- 
manent retention of an embryonic type of structure, or as an 
approximation to the characters of the Reptiles. Another 
remarkable point in connection with A7vcheopteryx, mm which 
it differs from all known Birds, is, that the wing was furnished 
with two free claws. From the presence of feathers, Avche- 
opteryx may be inferred to have been hot-blooded ; and this 
character, taken along with the structure of the skeleton of the 
wing, may be held as sufficient to justify its being considered 
as belonging to the class of Birds. In the structure of the 
tail, however, it is singularly Reptilian ; and there is reason to 
believe that its jaws were furnished with teeth sunk in distinct 
sockets, as is the case in no existing Bird. This conclusion, 
at any rate, is rendered highly probable by the recent discovery 
of “ Toothed Birds” (Odontornithes) in the Cretaceous rocks 
of North America. 
The Wammats of the Jurassic period are known to us by 
a number of small forms which occur in the “Stonesfield 
Slate” (Great Oolite) and in the Purbeck beds (Upper 
Oolite). The remains of these are almost exclusively sepa- 
rated halves of the lower jaw, and they indicate the existence 
during the Oolitic period in Europe of a number of small 
‘“‘Pouched animals” (JZarsupials). In the horizon of the 
Stonesfield Slate four genera of these little Quadrupeds have 
been described —viz., Amphilestes, Amphitherium, Phascolo- 
thertum, and Stereognathus. In Amphitherium (fig. 183), the 
molar teeth are furnished with small pointed eminences or 
‘cusps ;” and the animal was doubtless insectivorous. By 
Professor Owen, the highest living authority on the subject, 
Amphitherium is believed to be a small Marsupial, most 
nearly allied to the living Banded Ant-eater (JZyrmecobius) of 
Australia (fig. 158).  Amphilestes and Phascolotherium (fig. 
184) are also believed by the same distinguished anatomist 
and paleontologist to have been insect-eating Marsupials, and 
