312 OOLITIC GROUP [Oh. XX 



Owen has since established its generality in the entire marsupial series. 

 In all these pouched quadrupeds, this process is turned inwards, as at c d, 

 fig. 380, in the Brazilian opossum, whereas in the placental series, as at c, 

 figs. 378 and 379, there is an almost entire absence of such inflection. 

 The Tupaia Tana of Sumatra has been selected by my friend Mr. Water- 

 house for this illustration, because that small insectivorous quadruped 

 bears a great resemblance to those of the Stonesfield Amphitherium. By 

 clearing away the matrix from the specimen of Amphitherium Prevostii 

 above represented (fig. 375), Prof. Owen ascertained that the angular pro- 

 cess (c) bent inwards in a slighter degree than in any of the known mar- 

 supialia ; in short, the inflection does not exceed that of the mole or 

 hedgehog. This fact turns the scale in favor of its affinities to the placental 

 insectivora. Nevertheless, the Amphitherium offers some points of approxi- 

 mation in its osteology to the marsupials, especially to the Myrmecobius, a 

 small insectivorous quadruped of Australia, which has nine molars on each 

 side of the lower jaw, besides a canine and three incisors.* 



Another species of Amphitherium has been found at Stonesfield (fig. 

 376, p. 311), which differs from the former (fig. 375) principally in being 

 larger. 



The second mammiferous genus discovered in the same slates was 

 named originally by Mr. Broderip Didelphys Bucklandi (see fig. 382), 



& 



J&i^ 



Phascolotherium Bucklandi, Broderip, sp. 

 a. Natural size. 6. Molar of same magnified. 



and has since been called Phascolotherium by Owen. It manifests a 

 much stronger likeness to the marsupials in the general form of the jaw, 

 and in the extent and position of its inflected angle, while the agreement 

 with the living genus Didelphys in the number of the premolar and molar 

 teeth is complete.f 



On reviewing, therefore, the whole of the osteological evidence, it will 

 be seen that we have every reason to presume that the Amplitherium 

 and Phascolotherium of Stonesfield represent both the placental and mar- 

 supial classes of mammalia ; and if so, they warn us in a most emphatic 

 manner, not to found rash generalizations respecting the non-existence of 

 certain classes of animals at particular periods of the past on mere nega- 

 tive evidence. The singular accident of our having as yet found nothing 

 but the lower jaws of seven individuals, and no other bones of their skele- 

 tons, is alone sufficient to demonstrate the fragmentaiy manner in which 

 the memorials of an ancient terrestrial fauna are handed down to us. 



* A figure of this recent Myrmecobius will be found in the Principles, chap. ix. 

 | Owen's British Fossil Mammals, p. 62. 



