130 SHELVE DISTRICT 



Ventral interior with widely placed teeth extending laterally on either side of the 

 delthyrium for about one-third the width of the pedicle valve, ventral subperipheral 

 rim ill-defined. Dorsal interior with sockets elongated parallel to the hinge-line, 

 dorsal adductor impressions limited to posterior half of the brachial valve. 

 Type material. 



length width (mm) 

 Holotype External and internal moulds of pedicle valve 



(BB 35488a, b) 6-8 9-0 



Paratypes External and internal moulds of brachial valve 



(BB 35489a, b) 5-2 8-o 



External and internal moulds of pedicle valve 



(BB 35490a, b) 5-5 7-5 



Incomplete external and internal moulds of 



conjoined valves (BB 35491a, b) - 10-5 



External mould of brachial valve (BB 35492) 5-0 - 



Horizon and locality. Hope Shales cropping out in Brithdir farmyard, 1 mile 

 ENE of Old Church Stoke (Grid Ref. SO 301953). 



Discussion. No other species has yet been described that can profitably be 

 compared with E. dissimulate/., and as the new species is represented by only a small 

 number of moulds few statistics can be compiled from the sample to indicate the 

 variability of diagnostic features. These are incorporated in the description. 



Family SOWERBYELLIDAE Opik 1930 

 Subfamily SOWERBYELLINAE Opik 1930 



SOWERBYELLA Jones 1928 

 Sowerbyella antiqua Jones emended A. W. 



(PL 22, figs. 4, 7-14 ; PI. 23, figs. 1, 3, 4) 



1928 Sowerbyella antiqua Jones : 419. 



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, 

 infrequently segregated into sectors with a mean width of 0-57 mm ; ventral muscle 

 scar extending forward for 32% of the length of the pedicle valve ; dorsal interior with 

 a median septum usually flanked by 3 pairs of lateral septa, extending anteriorly for 

 56% of the length of the brachial valve and commonly united into a raised platform 

 at the 4 mm growth stage. 



Description. Semicircular Sowerbyella with acute cardinal angles, planar or 

 very gently concave brachial valve 51% as long as wide, uniformly convex pedicle 

 valve 27% as deep as long (range 14% to 34% for 11 specimens) ; ventral and dorsal 

 interareas apsacline and anacline respectively with a supra-apical foramen and a 

 small pseudodeltidium and a complementary chilidium ; ornamentation almost 



