Thompson on Delphinus bidentatus. 221 



unfavourable to the support of animal life, so that at the time 

 when the siliceous matter was deposited in this district, there 

 were few or no shells around which it might aggregate. It 

 is perhaps this matter mixed up with the silex, to which the 

 Blackheath flints owe their peculiar character. 



The existence of beds of sand frequently discovered below 

 the Blackheath districts, proves the previous great agitation 

 of the waters, and that also must have contributed to diminish 

 the number of shells, but from their very great rarity some 

 destructive mixture seems to have been the most likely cause. 



In breaking open some of the Blackheath flints, masses of 

 red coloured gravel are found enclosed, and where there is no 

 possible opening by which gravel might have penetrated into 

 any hollow part left in the flint at its formation. The flint 

 has aggregated around the gravel, precisely in the same way 

 as in the chalk the flint is often found to have aggregated 

 round a mass of chalk, and to have enclosed it on all sides. 

 Specimens of this sort have been met with at Erith, more fre- 

 quently than at any other place; but they may be found in 

 other localities also. 



Art. IX. Upon the Identity of Hunters Delphinus bidentatus, 

 Baussard's Hyperoodon Honfloriensis, and Dale's Bottle Head 

 Whale. By W illiam Thompson, Esq. 



Bell in his late work upon the British Quadrupeds and Ce- 

 tacea, mentions in his preface that further information is re- 

 quired on many points of great interest in the history of the 

 latter, and he instances " the relation of the Hyperoodon of 

 Dale to that of Hunter," and Sir W. Jardine in his volume 

 upon Cetacea, pages 194 to 197, canvasses the question of 

 the identity of Hunter's and Baussard's Cetacean, leaving the 

 matter as it appears tome in greater doubt than ever. Where 

 doctors differ I should have thought it the height of presump- 

 tion to have introduced my humble opinion, were it not that 

 I have an opportunity of forming a judgment not afforded to 

 either of the eminent naturalists in question. Let me at once 

 then state that I conceive there is not a doubt of the identity 

 of Hunter's and Baussard's specimens, both of which were 

 females, and that I conceive Dale's specimen to be the male 

 of the same species ; for though from the figure given on page 

 493 of Bell's work, it appears to differ from the others in 

 form, being thicker in the shoulder, yet I conceive it does not 

 differ more than the bull does from the cow, or the male lion 

 from the lioness : as regards this last point of mine, however, 

 I confess I have nothing beyond surmise ; but the possible 



