26 SHELVE DISTRICT 



Horizon and locality. Hope Shales exposed in path west of Brithdir Farm, 

 i mile ENE of Old Church Stoke (Grid Ref. SO 300953). 



Discussion. The attribution of relatively small obolids found in the Hope Shales 

 to Obolus s.s. is a matter of convenience until more is known about the musculature 

 of the new species, which was not accommodated by well-developed platforms as in 

 more typical species. Even the identification of the species as an obolinid may be a 

 matter of dispute because the dorsal pseudointerarea does not bear an identifiable 

 median groove although it is certainly a better developed feature than the striated 

 thickening of the posterior margin characteristic of the glossellinid brachial valve. 

 In respect of both features, the new species differs from orthodox Obolus. However, 

 Cooper (1956 : 189-193) assigned a few species to the genus which bear some 

 resemblance to 0. subditivus. This is especially true of 0. ? biconvexa Cooper from 

 the Lower Paper ville Formation of Tennessee and the closely related 0. ? nitens 

 Cooper from the Lower Rich Valley Formation of Virginia, although both are more 

 elliptically elongate and lack radial plicae, while the former is further distinguished 

 by the presence of concentric undulations. 



Obolus sp. 



(PI. 1, figs. 9, 10) 



In contrast to 0. subditivus sp. nov., a few exfoliated valves have been recovered 

 from the Mytton Flags, which are more representative of typical Obolus. The ex- 

 posures in Bergam Quarry above Tankerville Mine (Grid Ref. SO 355995) have 

 yielded an evenly convex pedicle valve (BB 35581a, b) about 6 mm long, which is 

 transversely oval in outline with a length about 70% of the width and a depth 25% 

 of the length. A heart-shaped postero-medial portion of the valve has broken away 

 and probably constitutes the muscle platform. No identifiable impressions are 

 preserved on the internal mould of the platform but a well-defined pedicle groove is 

 seen medially indenting a relatively narrow pseudointerarea. 



Another incomplete specimen (BB 35582) about 8 mm wide and over 1 mm deep 

 has been collected from near an adit 290 yds. west of Wood House (Grid Ref. 

 SJ 336002). It bears a pair of submedial muscle scars and may be the brachial 

 valve of the same species. Even so, paucity of material precludes specific identifica- 

 tion. 



SCHMIDTITES Schuchert & Le Vene 1929 



Schmidtites ? simplex sp. nov. 

 (PL 1, figs. 11-15) 



Diagnosis. Subequally biconvex, circular obolids with valves almost as long as 

 wide and 10% as deep as long, ornamented by fila and overlapping lamellae ; 

 pseudointerareas narrow, probably striated and divided by relatively wide pedicle 

 groove and median dorsal depression. 



Description. Subequally biconvex, circular obolids with inconspicuous beaks and 

 valves 99% as long as wide and 10% as deep as long ; ornamented by strong fila, 



