Ch. XX.] STOXESFIELD MAMMALIA— STEREOGXATHUS. 409 



points of approximation 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, hesides a canine 

 and three incisors.* 



Another species of Amphitherium has been found at Stonesneld 

 (fig. 413, p. 407), which differs from the former (fig. 412) principally 

 in being larger. 



The second mammiferous genus discovered in the same slates was 

 named originally by Mr. Broderip Didelphys BucMandi (see fig. 419), 



Fio;. 419. 



Phascolotherium BucMandi, Broderip, sp. 

 a. ^Natural size. &. 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 pre- 

 molar and molar teeth is complete.f 



In 1854 the remains of another mammifer, small in size, but larger 

 than any of those previously known, was announced by Mr. Charles- 

 worth to the British Association as having been obtained many years 

 before from the Stonesfield slate by the Eev. J. P. Dennis. This fossil, 

 to which the generic name of Stereognathus was given, consisted, as 

 is usually the case in these old rocks (see above, p. 385), of part of a 

 lower jaw, in which were implanted three double-fanged teeth, differ- 

 ing in structure from those of all other known recent or extinct mam- 

 mals. According to Professor Owen, the molar of Pliolophus, a small 

 extinct herbivorous genus of the London clay, makes the nearest ap- 

 proach to it. The form and structure of the teeth in Stereognathus 

 seemed to imply that this quadruped possessed a higher organization 

 than any other secondary mammal yet discovered, but the doubts 

 entertained respecting its true affinities afford a somewhat disappoint- 

 ing illustration of the limited extent to which Cuvier's law of cor- 

 rellation or the coexistence of animal structures is available in palse- 

 ontology. Given a lower jawbone with three perfect molar teeth, 

 having two or more fangs each implanted in separate sockets, to find 

 the rest of the organization, or at least to determine the family and 

 sub-class to which the animal belonged — such being the problem, 

 Professor Owen tells us that he believes that Stereognathus was hoofed, 

 herbivorous, and placental, but he adds, that for anything that physio- 



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

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



