The examples of mammalia, above alluded to, are confined to the Trias and the Oolite. In the former, the evidence is as yet limited to two small molar teeth, described by Professor Plieninger in 1847, under the generic name of Microlestes. They were found near Stuttgart, and possess the double fangs so characteristic of mammalia.[217] The other fossil remains of the same class were derived from one of the inferior members of the oolitic series in Oxfordshire, and afford more full and satisfactory evidence, consisting of the lower jaws of three species of small quadrupeds about the size of a mole. Cuvier, when he saw one of them (during a visit to Oxford in 1818), referred it to the marsupial order, stating, however, that it differed from all known carnivora in having ten molar teeth in a row. Professor Owen afterwards pointed out that the jaw belonged to an extinct genus, having considerable affinity to a newly discovered Australian mammifer, the _Myrmecobius_ of Waterhouse, which has nine molar teeth in the lower jaw. (Fig. 9.) A more perfect specimen enabled Mr. Owen in 1846 to prove that the inflection of the angular process of the lower jaw was not sufficiently marked to entitle the osteologist to infer that this quadruped was marsupial, as the process is not bent inwards in a greater degree than in the mole or hedgehog. Hence the genus amphitherium, of which there are two species from Stonesfield, must be referred to the ordinary or placental type of insectivorous mammals, although it approximates in some points of structure to the myrmecobius and allied marsupials of Australia. The other contemporary genus, called phascolotherium, agrees much more nearly in osteological character and precisely in the number of the teeth with the opossums; and is believed to have been truly marsupial. (Fig. 10.) [Illustration: Fig. 10. _Natural size._ Phascolotherium Bucklandi, _Owen_. (_Syn._ Didelphis Bucklandi, _Brod._) Lower jaw, from Stonesfield.[220] 1. The jaw magnified twice in length. 2. The second molar tooth magnified six times.] The occurrence of these most ancient memorials of the mammiferous type, in so low a member of the oolitic series, while no other representatives of the same class (if we except the microlestes) have yet been found in any other of the inferior or superior secondary strata, is a striking fact, and should serve as a warning to us against hasty generalizations, founded solely on negative evidence. So important an exception to a general rule may be perfectly consistent with the conclusion, that a small number only of mammalia inhabited European latitudes when our secondary rocks were formed; but it seems fatal to the theory of progressive development, or to the notion that the order of precedence in the creation of animals, considered chronologically, has precisely coincided with the order in which they would be ranked according to perfection or complexity of structure.