ORDOVICIAN BRACHIOPODA 109 



Cardinal process with bilobed myophore and long shaft on well-developed noto- 

 thyrial platform passing anteriorly into median ridge ; brachiophores triangular in 

 outline, acutely divergent, brachiophore bases parallel, ankylosed to median ridge 

 and extending anteriorly for 15% of the length of the brachial valve, sockets oblique, 

 bounded ventrally by brachiophores but not defined laterally by fulcral plates ; 

 quadripartite adductor scars 46% as long as the valve ; adjustor scars small oval, 

 located on median ridge anterior to notothyrial platform, mantle canal pattern 

 lemniscate. 



Figured material. 



Internal mould of brachial valve (BB 35305) 

 Internal mould of pedicle valve (BB 35306) 

 External mould of brachial valve (BB 35307) 

 External mould of brachial valve (BB 35308) 

 Internal mould of brachial valve (BB 35309) 

 Incomplete internal mould of brachial valve (BB 35310) 

 External and internal moulds of pedicle valve (BB 35311a, b) 

 External and internal moulds of pedicle valve (BB 35312a, b) 

 External and internal moulds of brachial valve (BB 35313a, b) 

 External and internal moulds of brachial valve (BB 35314a, b) 

 External and internal moulds of brachial valve (BB 35315a, b) 



Horizons and localities. BB 35305-35310 from Lower Llanvirn ashy shales 

 exposed in stream 240 yds west of Llwyn Bedw Farm, Llandeilo (Grid Ref. 

 SN 653212) ; BB 35311, BB 35314, BB 35315 from Weston Beds exposed 210 yds 

 south-east of road crossing Betton Dingle, Lyde (Grid Ref. SJ 317015) ; BB 35313 

 from Weston Beds at Cwm Dingle 640 yds south of Little Weston (Grid Ref. 

 SO 294978) ; BB 35312 from Weston Beds in road exposure 430 yds south-west of 

 Miner's Arms, Priestweston (Grid Ref. SO 291970). 



Tissintia immatura (Williams) emended A. W. 



(PI. 18, figs. 10, 12-15 ; PL 19, figs. 1-5) 



1949 Resserella immatura Williams : 165. 



Diagnosis. Subcircular, planoconvex Tissintia with subcarinate pedicle valve 

 31% as deep as long, costellae reflexed posteriorly along the hinge-line and commonly 

 numbering 3 per mm 5 mm antero-medially of the dorsal umbo ; brachiophore 

 bases normally thickened to extend anteriorly for 17% of the length of the brachial 

 valve and 84% of their lateral spread ; ventral muscle field elongately bilobed 

 extending forward for 38% of the length of the pedicle valve. 



Description. Subcircular, planoconvex to more rarely ventribiconvex with 

 obtuse cardinal angles ; pedicle valve 31% as deep as long with a slightly carinate 



length 



width (mm 



6-0 



7-0 



9-0 



io-o 



7-5 



9-0 



8-o 



9-5 



14-0 



16-0 



14-0 



20-5 



12-5 



15-0 



13-0 



20-0 



13-0 



16-0 



12-0 



14-0 



