78 SHELVE DISTRICT 



Platystrophia cf. major Williams 1955 

 (PL 13, figs. 1, 2, 4) 



1955 Platystrophia precedens McEwan major Williams : 402. 



The moulds of two immature valves of 'Platystrophia lacking the distinctive 

 concentric ornamentation of P. caelata sp. nov. have also been found in the Shelve 

 area. They are the moulds of a brachial valve nearly 5 mm long (BB 35586a, b) 

 from Aldress Shales exposed in the bank of Ox Wood Dingle at the south-west corner 

 of Ox Wood a few yards north of the Rorrington-Wotherton road (Grid Ref. 

 SJ 290007), and a pedicle valve 5-5 mm long (BB 35587a, b) from the Spy Wood 

 Grit exposed on top of the ridge 1440 yds NNE of the Rorrington bench mark 599 

 (Grid Ref. SJ 303018). Neither valve can be completely reconstructed from the 

 indifferently preserved moulds but the brachial valve appears to have been about 

 80% as long as wide and 20% as deep as long with a well-defined rounded fold about 

 40% as wide as the valve. The radial ornamentation consists of 3 costae on the 

 fold and 5 on each lateral slope with a wavelength of 07 mm, 5 mm antero-medially 

 of the umbo. Only impressions of subparallel brachiophore bases and a blade-like 

 cardinal process are preserved internally. The pedicle valve was similarly orna- 

 mented, although traces of fine concentric lamellae are also sporadically preserved, 

 while internally the ventral muscle scar extended well beyond the slightly divergent 

 dental plates for 36% of the valve length. 



These few statistics and especially the presence of 3 costae on the fold and 2 in 

 the sulcus suggest that both valves may be provisionally assigned to P. major 

 Williams (in Whittington & Williams 1955 : 402) first described from the Derfel 

 Limestone of N. Wales. The species is morphologically like the American species 

 P. precedens McEwan but is now also known from the Upper Llandeilo (MacGregor 

 1961 : 184). New evidence on intraspecific variability in the arrangement of costae 

 suggests that the species is more likely to be related to the Platystrophia dentata 

 (Pander) group from the Baltic (Williams 1963 : 371). 



MCEWANELLA Foerste 1920 

 Mcewanella sp. 



(PL 13, figs. 3, 5) 



An incomplete pedicle valve (BB 35416) and a deformed internal ventral mould 

 (BB 35417) from the Whittery Shales exposed in the stream at the north end of 

 Spring Coppice 865 yds south-east of Hockleton Bridge (Grid Ref. SO 279997) are 

 the only specimens of Mcewanella so far recovered in the Shelve area. 



Growth lines on the valve which was about half as deep as long, and shallowly 

 sulcate antero-medially, indicate that the outline changed from semi-circular to 

 subquadrate during growth, because the immature valve was widest along the 

 mucronate hinge-line whereas fully developed valves were about as wide as long with 

 the maximum width well anterior of the hinge line with its orthogonal cardinal 

 angles. The external surface was ornamented by branching costellae numbering 



