Mr. J. G. Jeffreys on Chemnitzia Gulsonse. 27 



tions of physical conditions from river or lake to estuary and sea 

 prevailed. 



2nd. That the upper lacustrine strata exhibit such alternations, 

 is shown by bed No. 2, but still more clearly by the section at 

 Hampstead Cliff, which belongs to this group. The consider- 

 ation of its beds does not fall within the limits of our section, 

 belonging as they do to a higher zone in the upper lacustrine 

 seiies. The lower lacustrine beds present similar phsenomena. 



3rd. That the estuaiy conditions more especially prevailed 

 before and after the deposition of the intercalated marine bed. 



4th. That the upper marine indicates a period in the struggle 

 between sea and lake, when the former obtained for a time the 

 supremacy : the marine shells and sharks' teeth it contains prove 

 this condition. 



5th. The white and yellow sands at Alum Bay immediately 

 overlying the Barton group were probably of estuary origin. The 

 absence of organic remains leaves a doubt upon the subject. The 

 equivalent bed however at Beacon Cliff on the Hampshire coast, 

 which I shall more particularly describe in a future communi- 

 cation, contains a large quantity of estuaiy shells mixed with 

 true marine genera, together with the bones of turtles and 

 the teeth of sharks. Guided by these facts, we infer that the 

 white and yellow sands of Headon Hill were the great estuary 

 deposit which introduced the lacustrine conditions under which 

 the lower freshwater group, with the other intercalated estuary 

 beds, were de])Osited. 



III. — Note on the Chemnitzia Gulsonse of Clark. 

 By J. GwYN Jeffreys, Esq., F.E-.S. 



To the Editors of the Annals of Natural History. 



Gentlemen, 



While thus publicly expressing the thanks which, in common 

 with I believe all others who take an interest in the study of 

 the British Mollusca, I owe to my old and esteemed friend Mr. 

 Clark, for his valuable papers which have lately appeared in the 

 'Annals of Natural History,' I cannot forbear also expressing 

 my opinion that the shell which he has described and named in 

 the last number as Chemnitzia Gulsonee, does not belong to the 

 genus Chemnitzia. ]\Iy specimens do not show the slightest 

 inversion of the apical whorls ; nor does that character appear 

 to exist in Jeffreysia diaphana, of which I have purposely exa- 

 mined about a hundred specimens, any more than in the Rissoee. 

 The peristome too is continuous in adult specimens of both those 

 shells, which is not the case in Chemnitzia or Odostomia. To the 



