98 SHELVE DISTRICT 



length width (mm) 

 Paratypes External and internal moulds of pedicle valve 



(BB 35353a, b) 2-5 3-5 



External and internal moulds of pedicle valve 



(BB 35354a, b) i-8 



External and internal moulds of brachial valve 



(BB 35355a, b) 3-0 



External and internal moulds of brachial valve 



(BB 35356a, b) 2-0 3-0 



External and internal moulds of brachial valve 



(BB 35357a, b) 2-5 



Type horizon and localities. Mytton Flags (Shelve Church Member) : 

 BB 35353a, b from exposures in road level north of Wood House (Grid Ref . S J 338003) , 

 all other specimens from a trench cut 1 ft above road level near Shelve Church (Grid 

 Ref. SO 335990). 



Discussion. Among the fossils recovered from the Mytton Flags, there quite 

 commonly occur impressions of a small costellate, thin-shelled orthide which have 

 all the essential characters expected of early enteletaceans. The combination of 

 such features is so striking that, although there is, as yet, no proof, such as the pre- 

 sence of microscopic moulds of puncta, of their enteletacean affinities, they have been 

 identified as primitive Dalmanella. Certainly they are strongly reminiscent of 

 young Dalmanella in many respects, yet there are characters that immediately 

 distinguish these Arenig forms from all other described Dalmanella. Among these 

 are the fineness and simple arrangement of costellae and the ridge-like cardinal 

 process which did not extend the length of the notothyrial platform nor become 

 differentiated into myophore and shaft as in other species assigned to the genus. 

 Not only do these features render the new species unique among known Dalmanella 

 but, together with the obscurity of muscle impressions and simplicity of brachio- 

 phore arrangement, are also the features one would expect to find in a stock that was 

 ancestral to the more typical Ordovician Dalmanella. Indeed when more is known 

 about these Arenigian stocks, they may prove to be so distinctive in the generalized 

 nature of their cardinalia as to constitute a distinct species group within the 

 Dalmanella taxon. 



ONNIELLA Bancroft 1928 



Onniella ostentata Williams lepida subsp. nov. 



(PI. 16, figs. 9-14) 



Diagnosis. Like Onniella ostentata Williams (1963 : 405) but with finer costellae 

 numbering 4 to 6 per mm at the 5 mm growth stage, shorter dental plates which 

 grew forward more slowly and a massive bilobed cardinal process not united to the 

 brachiophores in adult shells. 



