721 



MARSUPIATA. 



MARSUPIATA. 



723 



spurious molars in every genus of the placental Ferce have two fangs, 

 and the whole of them in the Marsupialia. If the ascending ramus 

 in the Stonesfield jaws had been absent, and with it the evidence of 

 their mammiferous nature afforded by the condyloid, coronoid, and 

 angular processes, Professor Owen stated that he conceived the teeth 

 alone would have given sufficient proof, especially in their double fangs, 

 that the fossils do belong to the highest class of animals. 



In reply to the objections founded on the double fangs of the 

 Basilosaurus, Professor Owen said that the 'icharacters of that fossil 

 not having been fully given, it is doubtful to what class the animal 

 belonged ; and in answer to the opinion that certain sharks have double 

 fangs, he explained that the widely bifurcate basis supporting the tooth 

 of the shark is no part of the actual tooth, but true bone, and ossified 

 parts of the jaw itself, to which the tooth is anchylosed at one part, 

 and the ligaments of connection attached at the other. The form, 

 depth, and position of the sockets of the teeth in the Thylacothere 

 are precisely similar to those in the small Opossums. The colour of 

 the fossils, Professor Owen said, could be no objection to those 

 acquainted with the diversity in this respect, which obtains iu the 

 fossil remains of Mammalia. Lastly, with respect to the Thylacothere, 

 the author stated that the only trace of compound structure is a mere 

 vascular groove running along its lower margin, and that a similar 

 structure is present in the corresponding part of the lower jaw of 

 some species of Opossum, of the Wombat, of the Balcena antarctica, 

 and of the Myrmecobius, though the groove does not reach so far 

 forward in this animal ; and that a similar groove is present near 

 the lower margin, but on the outer side of the jaw, in the Sorex 

 Indicia. 



Phaicolotherium, Owen, is another genus of fossil Marsupiata. 

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

 right ramus of tne 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 and figured by Mr. Broderip 

 (1828, with the provision* name of Didelphys Bucklandii) in the 

 ' Zoological Journal," and its distinction 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 thegenera 

 Didelphys and Dasyurus. In its being on a level with the molar teeth, 

 it corresponds with the marsupial genera Dasyurua and Thylacynus, 

 OB well as with the placental Zoophaga. The general form and pro- 

 portions of the coronoid process closely resemble those iu zoophagous 

 Marsupials ; but in the depth and form of the entering notch, between 

 the process and the condyle, it corresponds moat closely with the 

 Thylacynui. Judging from the fractured surface of the inwardly 

 reflected angle, that part had an extended oblique base, similar to 

 the inflected angle of the Thylacynui. In the Phaicolotherium the 

 flattened inferior surface 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 Thylacynui and 

 Dofyurut; but this difference is not one which approximates the 

 fossil in question to any of the placental Zoophaga ; on the contrary, 

 it is in the marsupial genus Phatcolomys, 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 Pbascolothere, like the Thylacothere, differs from 

 all zoophagous Marsupials and the placental fene ; but in the Hypti- 

 prymnui and Phascolomys, marsupial herbivora, the orifice of the dental 

 canal is situated, as in the Stonesfield fossils, very near the vertical 

 line dropped from the last molar teeth. The form of the eymphysis, 

 in the Phascolothere, cannot be truly determined : but Professor Owen 

 stated his opinion that it resembles the symphysis of the Didelpltys 

 more than that of the Datyurvi or Thylacynui. 



Professor Owen agrees with Mr. Broderip in assigning four incisors 

 to each ramui of the lower jaw of the Phascolothere, as in the Didel- 

 phyi ; but in their scattered arrangement they resemble the incisors 

 of the Myrmecobiui. 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 hindennost molar, the 

 Phascolothere resembles the Myrmecobiut more than it does the 

 (Jpottum, Datyurui, or Thylacynui ; but in the form of the crown the 

 molars of the fossil resemble the Thylacynut more closely than any 

 other genus of Marsupials. In the number of the grinders the Phas- 

 colothere resembles the Opossum and Tliylacinut, having four true and 

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

 differ from those of the Opottum and Thylacothere in wanting a pointed 

 tubercle on the inner side of the middle large tubercle, and in the 

 same transverse 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 a little beyond the anterior and posterior smaller 

 cusps, giving the quinquecuspid appearance to the crown of the tooth. 

 This ridge, which in P/iaicolotherium represents the inner cusps of the 

 true molars in Viddphyi and Thylacotherium, is wanting in Thylacynui, 

 in which the true molars are more simple thau in the Phascolothere, 

 though tmrdly less distinguishable from the false molars. In the 

 second true molar of the Phascolothere 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 the Thylacinut; but in the 



HAT. HIST. CIV. VOT,. III. 



Thylacinus the two posterior molars increase in size, while in the 

 Phascolothere they progressively diminish, as in the Myrmecobius. As 

 ;he outer sides of the grinders in the jaw of the Phascolothere are 

 mbedded in the matrix, we cannot be sure that there is not a smaller 

 cuspidated ridge sloping down towards that side, as in the crowns of 

 ;he teeth of the Myrmecolius. But assuming that all the cusps of the 

 teeth of the Phascolothere are exhibited in the fossil, still the crowns 

 of these teeth resemble those of the Thylacinus more than they do 

 ;hose of any placental Insectivora or Phoca, if even the form of the 

 aw permitted a comparison of it with that of any of the Seal tribe. 

 Connecting then the close resemblance which the molar teeth of the 

 Phascolotherium bear to those of the Thylacynus with the similarities 

 of the ascending ramus of the jaw, Professor Owen is of opinion that 

 the Stonesfield fossil was nearly allied to Thylacynus, and that its 

 Dosition in the marsupial series is between Thylacynus and DidelpTiys. 

 With respect to the supposed compound structure of the jaw of the 

 Phaicolotherium, Professor Owen is of opinion that of the two linear 

 impressions which have been mistaken for harmonise, or toothless 

 sutures, one, a faint shallow linear impression continued from between 

 the ante-penultimate and penultimate molars obliquely downwards 

 and backwards to the foramen of the dental artery, is due to the 

 pressure of a small artery, arid he stated that he possessed the jaw of 

 a Didelphys Virginiana which exhibits a similar groove in the same 

 Dlace. Moreover this groove in the Phascolothere does not occupy the , 

 same relative position as any of the costiguous margins of the oper- 

 cular and dentary pieces of the reptile's jaw. The other impression 

 In the jaw of the Phascolotherium is a deep groove continued from the 

 anterior extremity of the fractured tase of the inflected angle obliquely 

 downwards to the broken surface of the anterior part of the jaw. 

 Whether this line be due to a vascular impression or an accidental 

 fracture is doubtful ; but as the lower jaw of the Wombat presents an 

 impression in the precisely corresponding situation, and which is 

 undoubtedly due to the presence of an artery, Professor Owen conceives 

 that this impression is also natural in the Phascolothere, but equally 

 unconnected with a compound structure of the jaw; for there is not 

 any suture in the compound jaw of a reptile which occupies a corres- 

 ponding situation. 



The most numerous, the most characteristic, and the best-marked 

 sutures in the compound jaws of a reptile are those which define the 

 limits of the coronoid, articular, angular, and surangular pieces, and 

 which are chiefly conspicuous on the inner side of the posterior part 

 of the jaw. Now the corresponding surface of the jaw of the Phas- 

 colothere is entire; yet the smallest trace of sutures, or of any 

 indication that the coronoid or articular processes were distinct pieces, 

 cannot be detected ; these processes are clearly and indisputably con- 

 tinuous, and confluent with the rest of the ramus of the jaw. So 

 that where sutures ought to be visible, if the jaw of the Phascolothere 

 were composite, there are none ; and the hypothetical sutures that 

 are apparent do not agree in position with any of the real sutures of 

 an oviparous compound jaw. 



Lastly, with reference to the philosophy of pronouncing judgment 

 on the Saurian nature of the Stonesfield fossils from the appearance 

 of sutures, Professor Owen offered one remark, the justness of which, 

 he said, would be obvious alike to those who were and to those who 

 were not conversant with comparative anatomy. The accumulative 

 evidence of the true nature of the Stonesfield fossils, afforded by the 

 shape of the condyle, coronoid process, augle of the jaw, different 

 kinds of teeth, shape of their crowns, double fangs, implantation in 

 sockets the appearance, he repeated, presented by these important 

 particulars cannot be due to accident ; while those which favour the 

 evidence of the compound structure of the jaw may arise from 

 accidental circumstances. (' Qeol. Proc.,' 1838-39, vol. iii.) 



Jaw of Phaacoloilierium liueJtlaniii. Upper figure magnified. 



A paper was afterwards read, entitled ' Observations on the Struc- 

 ture and Relations of the presumed Marsupial Remains from the 

 Stonesfield Oolite, by William Ogilby, Esq., F.G.S.' 



These obpervations were intended by the author to embody only 

 the most prominent characters of the fossils, and those essential points 

 of structure in which they are necessarily related to the class of 

 mammifers or of reptiles respectively. For the sake of putting tha 



3 A 



