132 SHELVE DISTRICT 



2 mm antero-medially of the umbones of 3, 6, 10, 7 and 1 brachial valves respectively, 

 and segregated into sectors by thickened costellae in only 2 out of 27 valves. 



Teeth small, dental plates obsolescent, cordate ventral muscle field 62% as long 

 as wide and extending forward for 26% of the length of the pedicle valve ; muscle 

 scars and mantle canal system differentiated as in S. antiqua s.s. 



Cardinalia consisting of a median cardinal process fused with chilidial plates and 

 widely divergent socket plates extending anteriorly for 10% of the length of the 

 brachial valve and for an average of 28% of their lateral spread in 6 valves (range 

 2 5% to 35%) ; notothyrial platform poorly developed ; lophophore and muscle 

 supports consisting of a median septum flanked by 3 pairs of lateral septa, rarely 

 more or fewer, united by secondary shell into a cleft platform in 2 out of 13 specimens 

 over 3-5 mm long. 



Figured material. 



External mould of brachial valve (BB 35535) 



Incomplete external mould of brachial valve (BB 35536) 



Internal mould of pedicle valve (BB 35537a) 



External mould of pedicle valve (BB 35537b) 



Internal mould of brachial valve (BB 35538) 



Internal mould of pedicle valve (BB 35539) 



Incomplete internal mould of pedicle valve (BB 35540) 



Internal and incomplete external moulds of brachial valve 



(BB 3554ia, b) 



Incomplete internal mould of brachial valve (BB 35542) 



Horizon and locality. Flags transitional from the Meadowtown to Betton 

 Beds exposed in a ploughed field 180 yds south-west of a wall in side of lane from 

 Meadowtown to Castle Ring (Grid Ref. SJ 310009). 



Sowerbyella multiseptata sp. nov. 



(PI. 23, figs. 14-19 : PL 24, figs. 1, 3) 



Diagnosis. Semicircular Sowerbyella with a brachial valve 51% as long as wide, 

 external surface very rarely ornamented by impersistent rugae, finely parvicostellate 

 with a modal count of 10 ribs per mm, 2 mm antero-medially of the dorsal umbo ; 

 ventral muscle scar extending forward for 32% of the length of the pedicle valve ; 

 dorsal interior with a late-developing median septum usually flanked by 3 pairs of 

 lateral septa extending anteriorly for 73% of the length of the brachial valve. 



Description. Semicircular Sowerbyella with acute, rarely orthogonal, cardinal 

 angles ; brachial valve 51% as long as wide uniformly gently concave, occasionally 

 with a narrow median fold extending from a protegulum 0*2 mm long to die out 

 anteriorly ; pedicle valve convex, rarely subcarinate, with a mean depth of 17% 

 relative to the length of 4 valves (range 16% to 19%) ; ventral and dorsal interareas 

 apsacline and anacline respectively with a supra-apical foramen and a small pseudo- 

 deltidium and complementary chilidium ; ornamentation almost exclusively finely 

 parvicostellate with counts of 8, 9, 10 and 11 ribs per mm, 2 mm antero-medially of 



length 



width (mm) 



2-5 



5-5 



2-3 



- 



3-o 



6-o 



2-8 



5-8 



2-5 



5-2 



3-o 



5-5 



4-3 



— 



4-3 



8-o 



2-5 



- 



