364 



A. J. Jukea-Broinie — Two Stages in Ujjper Chalk. 



lu considering this table, if in the first place we leave the Ojfaster 

 zone out of account we find that the three lower zones have yielded 

 forty-eight species and that the two higher zones contain no fewer 

 than fifty-six species. Of this large number only ten species and 

 varieties are common to the two assemblages, which are thus very 

 different, though, as might be expected, they are not so entirelj' distinct 

 as those of the more highly orj^anized Cephalopoda. 



The line of division between the two stages is not, however, so 

 clearly indicated by the Echinoderms, for the fauna of the Offaste^^ 

 zone seems to form a complete passage from the one to the other. 

 This zone has yielded fifteen species, of which ten range both up and 

 down, one ranges downward only, three range up but not down, 

 and one is restricted to the zone. The fact is that the tabulated 

 number of occurrences is hardly sufficient to give a reliable result, and 

 we can only infer that the zone might be placed in either stage. 



In passing to the South of France we come to a different area 

 of deposition, inhabited by an assemblage of Echinoderms which 

 differed considerably from that of the Anglo-Parisian basin. Some 

 of the northern species do occur in it, but there are a large number of 

 others. From the lists given by M. de Grossouvre, in the work already 

 mentioned, I have compiled a table of the distribution of species 

 in the Aquitaniau and Pyrenean areas, in order to ascertain what 

 evidence they afford. This list includes no fewer than one hundred 

 species, and yet is probably not quite complete ; the greater number 

 (sixty-three species) occur in the two higher zones and only ten 

 of these range down into the three lower zones. The equivalent 

 of the Offaster zone has yielded twenty-four species, and of these 

 ten range both upward and downward, three range down only, and 

 six pass up, while five are restricted. Here again, therefore, the 

 existence of two different faunas and consequently of two distinct 



