206 FOSSIL JAWS FROM STONESFIELD. 



groove is present near the lower margin, but on the outer side of the jaw, 

 in the Sorex Indicus. 



" Description of the half jaw of the Phascolotherium. — This fossil is a 

 right ramus of the lower jaw, having its internal or mesial surface exposed. 

 It once formed the chief ornament of the private collection of Mr. Broderip, 

 by whom it has since been liberally presented to the British Museum. It 

 was described by Mr. Broderip in the 'Zoological Journal,' and its distinc- 

 tion from the Thylacotherium clearly pointed out. The condyle of the jaw 

 ' is entire, standing in bold relief, and presents the same form and degree of 

 convexity as in the genera Didelphys and Dasyurus. In its being on a le- 

 vel with the molar teeth, it corresponds with the marsupial genera Dasyu- 

 rus and Thylacynus, as well as with the placental Zoophaga. The general 

 form and proportions of the coronoid process closely resemble those in zo- 

 ophagous marsupials ; but in the depth and form of the entering notch be- 

 tween the process and the condyle, it corresponds most closely with the 

 Thylacynus. Judging from the fractured surface of the inwardly reflected 

 angle, that part had an extended oblique base, similar to the inflected an- 

 gle of the Thylacynus. In the Phascolotherium, the flattened inferior sur- 

 face of the jaw, external to the fractured inflected angle, inclines outwards 

 at an obtuse angle with the plane of the ascending ramus, and not at an 

 acute angle, as in the Thylacyne and Dasyurus ; but this difference is not 

 one which approximates the fossil in question to any of the placental Zoo- 

 phaga : on the contrary, it is in the marsupial genus Phascolomys where a 

 precisely similar relation of the inferior flattened base to the elevated plate 

 of the ascending ramus of the jaw is manifested. In the position of the 

 dental foramen, the phascolothere, like the thylacothere, differs from all 

 zoophagous marsupials and the placental Ferm ; but in the Hypsiprymnus 

 and Phascolomys, marsupial Herbivora, the orifice of the dental canal is si- 

 tuated, as in the Stonesfield fossils, very near the vertical line dropped from 

 the last molar teeth. The form of the symphysis, in the Phascolotherium, 

 cannot be truly determined ; but Mr*. Owen is of opinion that it resembles 

 the symphysis of the Didelphys more than that of the Dasyurus or Thylacynus. 



" Mr. Owen agrees with Mr. Broderip in assigning four incisors to each 

 ramus of the lower jaw of the Phascolotherium, as in the Didelphys; but in 

 their scattered arrangement they resemble the incisors of the Myrmecobius. 

 In the relative extent of the alveolar ridge occupied by the grinders, and in 

 the proportions of the grinders to each other, especially the small size of the 

 hindermost molar, the Phascolotherium resembles the Myrmecobius more 

 than it does the opossum, Dasyurus, or Thylacynus ; but in the form of the 

 crown, the molars of the fossil resemble the Thylacynus more closely than 

 any other genus of marsupials. In the number of the grinders the Phasco- 

 lotherium resembles the opossum and Thylacynus, having four true and 

 three false in each maxillary ramus ; but the molares veri of the fossil differ 

 from those of the opossum and Thylacotherium in wanting a pointed tuber- 

 cle on the inner side of the middle large tubercle, and in the same trans- 

 verse line with it, the place being occupied by a ridge which extends along 

 the inner side of the base of the crown of the true molars, and projects be- 

 yond the anterior and posterior smaller cusps, giving the quinquecuspid 

 appearance to the crown of the tooth. This ridge, which, in Phascolothe- 

 rium, represents the inner cusps of the true molars in Didelphys and Thy- 

 lacotherium, is wanting in Thylacynus, in which the true molars are more 

 simple than in Phascolotherium, though hardly less distinguishable from the 

 false molars. In the second true molar of Phascolotherium, the internal 

 ridge is also obsolete at the base of the middle cusp, and this tooth presents 

 a close resemblance to the corresponding tooth in Thylacynus ; but in the 

 Thylacynus the two posterior molars increase in size, while in Phascolothe- 



