18 SHELVE DISTRICT 



each individual is, initially at least, represented in a death assemblage by two valves 

 so that counts of all specimens in collections consisting mainly of disarticulated valves 

 could be a gross misrepresentation of frequencies in vivo. Consequently the number 

 of individuals of listed species collected from each locality, shown in Tables i to II, 

 are the totals of, the more commonly occurring valves whether they are brachial or 

 pedicle. Also, the tables do not include localities yielding specimens of only one 

 species on the grounds that their distribution does not contribute to our under- 

 standing of the relationship within brachiopod associations. Such data may, 

 however, assist in identifying those species most tolerant of palaeoenvironmental 

 variation and have, therefore, been referred to in the explanatory text when this 

 possibility appears to hold. 



Table i shows the frequency distributions of various brachiopod species collected 

 from 22 localities of Mytton Flags. The fauna was dominated by an association 

 including Monobolina, Palaeoglossa and Lenorthis (each also occurring alone in 5, 5 

 and 2 localities respectively) which was especially prevalent in unlaminated micaceous 

 siltstones and fine-grained crystal tuffs. Another association of Dalmanella, 

 Protoskenidioides and Euorthisina was characteristic of laminated siltstones and 

 shales. The Monobolina association has a few elements in common with an associa- 

 tion involving Obolus, Paterula and Pseudolingula found in the dark grey micaceous 

 Hope Shales (Table 2). A similar lithofacies within the Stapeley Volcanic Group 

 (Table 3) supported another inarticulate association with Lingulella, Schmidtites and 

 Schizocrania, although Orthis and Desmorthis, which may have been constituents of 

 an association descended from the Arenig Dalmanella one, occur in crystal-lithic 

 tuffs. 



Table 2 



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

 from 7 localities of Hope Shales 



1234567 



Eocramatia dissimulata I — — I 4 — — 



Obolus subditivus -31 1 - 6 1 



Paterula cf. bohemica 1 1 1 - - 1 2 



Pseudolingula spatula - 1 - 1 - - 1 



Schizocrania salopiensis - 1 — - 1 1 - 



Table 3 



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

 from 5 localities of Stapeley Shales 



12345 



Conotreta stapeleyensis 4 — - - — 



Desmorthis ? sp. — 1 - 2 — 



Lingulella displosa petila — — 1 — 1 



Orthis sp. - 3 — - - 



Schizocrania salopiensis — — II — 



Schizotreta sp. - - - 1 - 



Schmidtites ? simplex subcircularis 1 - - - 1 



