200 



PROF. REYNOLDS AND MR. VAUGHAN ON THE [May I904, 



may have been recorded at another, and given a weight equal to that 

 of the commouest fossil at the horizon. In this way a completely- 

 deceptive difference between the two sections is falsely suggested. 



Bearing this fruitful source of error in mind, the appended table 

 may be considered to render as exact an account as is possible 

 of the range of the best-known Rhsetic mollusca at those sections 

 within the Bristol and Gloucestershire areas which have been most 

 exhaustively described. 



Table I. — Comparison of the Ranges of the typical Riletic Mollusca. 

 I II III IV V 



(a, a') 



(''to/) 



(ff, In (L k, I) O) 



Avicula contorta... - 



Pecte?i valoniensis 



Schizodus Ewaldi - 



Cardinal rhceticum 

 & C.cloacinum... 



Pylle Hill. 



Wainlode Cliff. 

 Garden Cliff. 1 

 S. Wales Line. 



Pylle Hill. 



Wainlode Cliff. 

 Garden Cliff. 

 S. Wales Line. 



Pylle Hill. 

 Wainlode Cliff. 

 Garden Cliff. 

 S. Wales Line. 



Pylle Hill. 

 Wainlode Cliff. 

 Garden Cliff. 



S. Wales Line. 



That the information conveyed by the above table may be as 

 exact as possible, the following remarks seem necessary : — 



Avicula contorta. — As a general rule, the determination of this 

 fossil is possible, even from very small fragments, on account 

 of its entire dissimilarity from the associated mollusca ; but in 

 I, where Plicatula cloacina is not uncommon, the determination 

 is rendered more difficult (see p. 203). 



Pecten valoniensis. —The determination of this fossil by an accurate 

 observer may be unhesitatingly accepted. 



1 We have ventured to dissent somewhat from Mr. Richardson's correlation 

 of the beds at Garden Cliff. Seeing that Avicula contorta and Schizodus occur 

 plentifully below his Bone-Bed (Bed 15), it does not appear to us that this bed 

 can be considered to be on the same horizon as that at Sodbury, which is well 

 below the level at which these mollusca commence to occur in any abundance. 

 It seems more probable that the section at Garden Cliff is one of the numerous 

 instances which illustrate the great variability of the position of the Bone-Bed. 



