ORDOVICIAN BRACHIOPODA 19 



The succeeding Weston and Betton Beds (Tables 4, 5) consist mainly of laminated 

 siltstones. They sustained an association which had evolved out of the Arenigian 

 Monobolina complex and was evidently ancestral to the Meadowtown assemblage. 

 In the Weston Beds, the association is dominated by Pseudolingula, Palaeoglossa 

 and Tissintia with the last occurring on its own in five localities additional to those 

 set out in Table 4. By Betton times, changes in the relative importance of species 

 had taken place so that the association was made up mainly of Palaeoglossa, Tissintia 

 and Schizomania with each of the last two stocks constituting the only brachiopods 

 found in three extra localities. 



Table 4 



The number of pedicle or brachial valves of the listed species recovered from 

 10 localities of Weston Beds 



123456789 10 



Palaeoglossa attenuata I I I — — i — — — i 



Pseudolingula spatula 1421 1211-12 



Schizocrania salopiensis 1--1 3 — — - — - 



Schizotreta ? sp. ____ 2 — — — — — 



Tissintia prototypa 14 - - - - - 115 3 4 



Table 5 



The number of pedicle or brachial valves of the listed species recovered from 11 localities of 



Betton Beds 



1 23456789 10 11 



Dalmanella salopiensis _________5_ 



Lingulella displosa _____ j _____ 



Palaeoglossa attenuata 2151111-1-1 



Paterula cf. bohemica _________ 1 _ 



Rafinesquina delicata _________6- 



Schizocrania salopiensis 1--1 1--1 1 - - 



Tissintia prototypa - 1 20 - — - 7 2 — — 5 



The Meadowtown Beds (Table 6) are essentially laminated calcareous siltstones or 

 fine-grained sandstones with subordinate calcarenites. This lithofacies was occupied 

 by an association derived from the later Llanvirn ones but incorporating new ele- 

 ments, so that the dominant forms were Palaeoglossa, Dalmanella, Rafinesquina, 

 Tissintia and Pseudolingula. Palaeoglossa was the only brachiopod occurring in 

 nine additional localities. The genus must have been more tolerant of variation in 

 the palaeoenvironment than its contemporaries because it is also the dominant 

 member (with Schmidtites) of an inarticulate association, descended from the early 

 Llanvirn communities, which includes Lingula, Paterula and Pseudolingula and is 

 found in rarely occurring medium grey shales and mudstones. 



The subordinate association identified in the Meadowtown Beds became over- 

 whelmingly important in the Rorrington lithofacies which consisted of medium to 

 dark grey slightly calcareous shales. The principal community (Table 7) was 



