ORDOVICIAN BRACHIOPODA 37 



3 specimens) ; muscle impressions including a pair of suboval umbonal scars situated 

 submedially and a pair of long lateral and transmedian muscle scars inserted on 

 either side of the median septum ; the two sets of scars extend anteriorly of the beak 

 for 20% and 43% of the valve length respectively ; postero-medial internal surfaces 

 of both valves sporadically and coarsely pitted. 



Type material. 



length width (mm) 



Holotype Incomplete external and internal moulds of 



brachial valve (BB 37124) 23-0 16 -o 



Paratypes External and internal moulds of brachial 



valve (BB 37125a, b) 10-5 6-5 



Internal mould of pedicle valve (BB 37126) 14-0 7-6 



External and internal moulds of brachial 

 valve (BB 37128a, b) 13-5 9-0 



Figured Incomplete exfoliated exterior of brachial 



specimen valve (BB 37129) - 7-6 



Type horizon and localities. Weston Beds : BB 37124 from exposures in 

 Cwm Dingle 640 yds south of Little Weston (Grid Ref. SO 294978) ; all other 

 specimens from outcrops 210 yds south-east of road crossing Betton Dingle, Lyde 

 (Grid Ref. SJ317015). 



Discussion. Pseudolingula is known to occur sporadically throughout much of 

 the Ordovician succession of the Shelve area, but only the Weston Beds have 

 yielded a sufficient number of specimens to allow some estimates to be made of 

 variability in the shape and internal structure of the shell. The valves known from 

 other horizons must also be provisionally referred to the same species as the Weston 

 material. Indeed an internal mould of a pedicle valve (BB 37130a, b) from the 

 Rorrington Beds exposed in Deadman's Dingle, 90 yds from the junction with Spy 

 Wood Dingle (Grid Ref. SO 289958), affords the only clear evidence of the nature of 

 the ventral posterior margin (PI. 4, fig. n), while an incomplete ventral interior 

 (BB 37129) from the Meadowtown Beds exposed at the side of Minicop Farm 

 (Grid Ref. SJ 314018), and a badly exfoliated valve up to 15 mm long (BB 35583) 

 from the Mytton Flags exposed in the River Camlad (Grid Ref. SO 320919), verify 

 the stratigraphic persistence of the characteristic ventral muscle platform and con- 

 centric ornamentation (PI. 4, figs. 12-14). 



In the absence of quantitative data on shell outline and proportions in described 

 Pseudolingula, the new species can only be distinguished, for the time being, by the 



Table 19 



Statistics of length (1) and maximum depth (w) of 18 brachial valves of Pseudolingula spatula 



sp. nov. from the Weston Beds 



1 mm (var 1) 11-84 (39' 1 6) 

 w mm (var w) 7-93 (16775) 



r 0-987 



a (var a) 0-6545 (0-00067) 



