70 ME. S. S. liUCKMAX OK [vol. lxXVl, 



none of the ammonites of the Dorset Coast. Correlation of the 

 Gloucestershire layer with C'inctce with the Dorset deposit in 

 Beds 111 and 113 seems to suggest itself; but it is below this 

 that the nodules with Phynchonella rostellata are found. One 

 would suppose that Ph. tlialia is of earlier date than Ph. rostel- 

 lata — a presumed dwarf development : ; but the Dorset evidence, 

 such as it is, suggests a later date, and that reading I have 

 adopted for Table I, where it seems to work sufficiently well. 



With regard to the brachiopod fauna, the following facts have 

 now been gathered : — 



(1) The geographical ranges of Cincta and of the two species of Rhyncho- 



nella (Tropiorhynchia) all vary. 



(2) Cincta. occurs in Dorset between Platypleuroceras above and Poly- 



morphites below. 



(3) Quenstedt and Oppel both place Terebratula nwmismalis (Cincta) on 



a different level from ammonites, and the Dorset evidence, in part 

 at any rate, supports this. 



And to these may be added other facts : — 



(4) Rhynchonella tlialia occurs in Normandy in an area but lately sub- 



merged, and with few or no ammonites. It occurs at Sodbury 

 (South Gloucestershire) in strata which follow a prolonged non- 

 sequence : all the strata from Raasayan 2, up to and including 

 Wessexian 5, are missing ; therefore it occurs in an area of fresh 

 submergence. It occurs under similar conditions in North Glou- 

 cestershire — that is after a period of elevation and erosion, for it 

 maybe noted that the record of Ammonites taylori for Cheltenham by 

 J. Buckman s (Phricocloceras, a single specimen), and a similar record 

 of it in Northamptonshire by Oppel, 3 show that, of the missing 

 strata, those of Wessexian 1 (Phricocloceras) at any rate were laid 

 down in the Severn- Valley area and beyond, but were almost 

 removed again. The finds may mean pockets of strata or remanie 

 specimens left behind : there is no Phricocloceras recorded by 

 Mr. Richardson, so the removal must have been fairly complete. 



Considering all these points, I am tempted to make the following 

 suggestion. The brachiopods under consideration lived, not 

 necessarily contemporaneously, but at intervals between the dates 

 of Platypleuroceras and Polymorph ites trivialis: the latter and 

 its allies occur in Wiirtemberg and widely throughout England ; 

 but, what is more important, they fail in Gloucestershire where 

 the brachiopod fauna is found so well developed. I suggest that 

 when these brachiopods lived there was a considerable deepening 

 of the Jurassic sea, marked by overstep in Normandy and Glouces- 

 tershire. This deepening of the sea was favourable to brachiopods 

 and unfavourable to ammonites. Ammonites must have lived 

 somewhere during these supposed brachiopod interludes ; but it 

 does not follow that the ammonites recorded in the Wessexian 

 scheme are the full sequence, nor that they were the strict con- 

 temporaries of the brachiopods : in fact, the evidence seems 



1 A further suggestion as to the affinity of these species is made later, 

 p. 90. 



2 I, 1, p. 91. 3 XIII, 1. p. 165. 



