part 4] 



EVOLUTION OF THE LIPAKOCEHATIDJK. 



253 



Middle Lias near Lincoln, and among them are bituberculate 

 developments of Oistoceras (7, p. 104). 



There are, therefore, not less than six -widely- separated horizons 

 with striatus-like forms, alternating* with beds containing the 

 different Capricorn ammonites from which they have respectively 

 evolved. Details of the correlation are given in Table I ; the 

 hemeral terms given for comparison are those recently proposed by 

 Mr. S. S. Buckman, to whom I am indebted for the loan of his 



Table I, showing the chief areas where Liparoceratid 



horizons are developed. 



Hemeral Terms 



Dorset 



Cheltenham 

 District 



Warwickshire 

 &N.GI05. 



Lincoln 



Yorkshire 



Zones 



Ranqes of Genera 



(MIDDLE LIAS 

 with liparoceratids) 



X 





X 







margaritatuszone 









Oistoceras 



X 







X 



X 



c 

 o 



N 



'3 



> 



re 



•o 



O'iStoceras 

 sub-zone 



j 









4 , ,1 



henleyi 



X 







X 





daedal icosta 

 sub-zone 





i 

 i 



davoei 



X 







X 





Liparoceras 



Becheiceras 



AnisoloWeras 



brevilobatum 





X 







? 



lataecosta 

 sub -zone 



lataScosta 



X 



X 



X 



X 



X 



i 

 i 

 in 



Beaniceras 



X 



X 



X 



X 



X 



ibex zone 



■n 

 2 

 .3 



O 



C 



u 



re 



Q- 





Androgynoceras 

 Oistocera 

 Aegoceras 

 Ambtycocera. 



carinatum 



X 



? 









cheltiense 



X 



X 





? 



X 



X 



valdani 



X 



X 



X 



X 





1 



1 



ibex 



X 



X 



X 





? 







1 

 1 















[The hemeral terras used are mainly those proposed by Mr. S. S. Buckman 

 in Q. J. G. S. vol. lxxiii (1917-18) pp. 264-266.] 



notes on the correlation of these beds. The corresponding sub- 

 zones are also shown. It must be borne in mind that an under- 

 standing of the relationships of the ammonites is only possible 

 when their horizons are accurately known ; the details of the 

 ammonite succession within the sub-zones must, therefore, be 

 studied. The best time-scale is obviously supplied by a sequence 

 of forms which are genetically connected, but a time-scale based 

 on an evolutionary series i or a number of such series) cannot 

 readily be constructed for the Liassic rocks of England, because, 

 except within small limits, the ammonites of the Lias did not evolve 

 here, our faunas probably representing successive immigrations. 

 Consequently, an ideal correlation is not at present possible. 



