the Fossil Jaws of Stonesfield. 641 



ought rather to be considered as constituting a new genus. — 

 With regard to its geological position, M. Prevost endeavours 

 to invalidate all the arguments of Dr. Buckland and other 

 English geologists, as to the age of the rock in which the 

 bones are found, and refuses to admit, as sufficiently proved, 

 the fact that the calcareous schist of Stonesfield really con- 

 stitutes a part of the oolitic series.. Thus the supposed 

 exception appears to be brought back within the rule, that 

 the bones of Mammalia are found in a fossil state, only in 

 the strata which are of more recent origin than the chalk. 



This explanation of so anomalous a fact was, however, en- 

 tertained but for a moment ; for Dr. Fitton, one of the most 

 distinguished English geologists, immediately showed, by a 

 very profound examination, that the rock which contained 

 the jaw-bones was certainly in the position, and forming a 

 part of the oolitic formation ; and from that time the paleon- 

 tological exception was re-admitted, although Mr. Samuel 

 Woodward appears to have forgotten it in his table of the fos- 

 sil remains of Great Britain. 



Some years after this the subject was renewed in a manner 

 which appeared still more plausible, and scarcely open to 

 objection, by a description and figure of the second half jaw 

 spoken of by Dr. Buckland, which, after having been lost for 

 some years, fortunately fell under the notice of Mr. Broderip. 

 He counted in it four incisors, one canine, and seven molars, 

 which is, in fact, the dental formula in the Didelphis ; and 

 having besides remarked that the teeth in the fragment de- 

 scribed by M. Prevost appeared to differ, not only specifi- 

 cally but generically from that which he had before him, Mr. 

 Broderip thought it necessary to make of his a distinct spe- 

 cies, which he very properly dedicated to Dr. Buckland, un- 

 der the name of Didelphis Bucklandii. 



From that time, that is to say, during the last ten years, all 

 the authors of treatises on Paleontology or Geology have ad- 

 mitted, as beyond all doubt, the existence of two species of 

 Didelphis, viz., the Did. Prevost it of Cuvier, and the Did. 

 Bucklandii of Broderip, occurring in the calcareous schist 

 of Stonesfield, which forms part of the oolitic series. 



In a note at the end of my memoir upon the antiquity of 

 the existing order of insectivorous Mammalia, I have already 

 declared my opinion concerning a portion of a lower jaw 

 brought from Stonesfield by M. Brochant de Villiers and his 

 pupils MM. Elie de Beaumont and Dufrenoy; and which had 

 been supposed to belong to the same Didelphis as the two 



