206 Geological Society. 



form structure, as in certain reptiles ; but, on reference to the fos- 

 sils, Mr. Owen states, it will be found that such is not the case, and 

 that the actual difference in the structure of the teeth strongly sup- 

 ports the mammiferous theory of the fossils. 



2. With respect to the argument founded on an interpretation of 

 structure, which really exists, the author showed, that the Thylaco- 

 therium, having eleven molars on each side of the lower jaw is no 

 objection to its mammiferous nature, because among the placental 

 carnivora, the Cams Megalotis has constantly one more grinder on 

 each side of the lower jaw than the usual number ; because the 

 Chrysochlore among the Insectivora has also eight instead of seven 

 molars in each ramus of the lower jaw ; and the Myrmecobius, 

 among the Marsupialia, has nine molars on each side of the lower 

 jaw ; and because some of the insectivorous Armadillos and zoopha- 

 gous Cetacea offer still more numerous and reptile-like teeth, with all 

 the true and essential characters of the mammiferous class. The ob- 

 jection to the false molars having two fangs, Mr. Owen showed 

 was futile, as the greater number of the spurious molars in every 

 genus of the placental /(?/'(^ 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, 

 Mr. 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, Mr. Owen said, that the characters of that fossil not 

 having been fully given, it is doubtful to what class the animal be - 

 longed ; and, in answer to the opinion, that certain sharks have 

 double fangs, he explained, that the widely bifurcate basis support- 

 ing 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 an- 

 chylosed at one part, and the ligaments of connexion attached at the 

 other. The form, depth and position of the sockets of the teeth in 

 the Thylacotliere are precisely similar to those in the small opos- 

 sums. The colour of the fossils, Mr. Owen said, could be no ob- 

 jection to those acquainted with the diversity in this respect, which 

 obtains in the fossil remains of Mammalia. Lastly, with respect to 

 the Thylacotliere, 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 IVombat, of the 

 Balcena antarctica, and of the Myrmecobius, though the groove does 



