﻿Vol. 6 1.] SEQUENCE IN THE BRISTOL AREA. 247 



K 2 , /3, Z x ; the typical form is rare in Z„ where it is 

 replaced by a mutation towards Pr. semireticidatus. 



(3) Productus semireticulatus. The mutation from Pr. Mar- 



tini occurs in Z v and becomes abundant in Z 2 . A 

 spinous mutation is characteristic of S x . 



(4) Productus aff. scabriculus (including two distinct varia- 

 tions ; the one Pr. cf. costatus, the other Pr. cf . semi- 

 reticulatus). Typical of Horizon e ; less common in D 2 . 



(iA) The Giganteid Producti (a group having subgeneric 

 value). 



(5) Productus aff. Cora [Dav.] (= Pr. corrugatus). Eare 



in Z and C ; abundant in S 2 ; common in D 1 and 

 extending on to Horizon e. 

 The different zones are characterized by distinct mutations (thus 

 mut. Z, mut. 0, mut. S 2 , and mut. D 1 are easily distinguished). 



Productus d is abundant in S L . 



(6) Productus gig anteus. Eare at the bottom of S 2 ; maximum 



at the top of S 2 and the bottom of D, ; extends on 

 into D 2 in a distinct mutation (' C7ionetijc>roductus'). 



(7) Productus hemisphericus. The typical form is only 



abundant at the top of S 2 and in D x . 



(ii) Chonetes. 

 Species-groups : — 



(1) Chonetes ' Bucliiana ' * (as figured by Davidson, 'Monogr. 



Brit. Paheoz. Brachiop.' Palseontogr. Soc. pi. lv,fig. 12) 

 has its maximum at the top of K x . 



(2) Chonetes cf . hardrensis : K ; Z ; C r 



Variants : — 



(a) Chonetes cf . crassistria. Rare in M ; very abundant in K ; 

 extends into Z v A somewhat similar form reappears in e. 



(b) Chonetes cf. lagaessiana. K and Z. 



(3) Chonetes papilionacea. Eare in Z x ; common in Z ; 



abundant at y, in C, and at intervals throughout S. 

 Variants : — 



(a) Chonetes cf. comoides is locally abundant in 0. 



(b) Chonetes aff. comoides is characteristic of D r 



Inarticulate Brachiopods. 



Lingula and (Discina). 

 Paucity of material has prevented any. attempt to separate the 

 forms which occur at different levels. 



1 I am not satisfied that this form is correctly referred to Chonetes Buchiana, 

 de Kon. 



s2 



