ordovician brachiopoda 123 



Type material. 



length width (mm) 



Holotype External and internal moulds of pedicle valve 



(BB 35342a, b) 9-3 n-2 



Paratypes Partly exfoliated pedicle valve with internal 



mould (BB 35343a, b) 12-0 



Internal mould of pedicle valve (BB 35344) n*5 14-5 



Incomplete external and internal moulds of 



brachial valve (BB 35345a, b) - - 



External and internal moulds of pedicle valve 



(BB 35346a, b) io-o 



Incomplete external and internal moulds of 



pedicle valve (BB 35347a, b) - - 



External and internal moulds of brachial valve 



(BB 35348a, b, c) 12-5 13-5 



External and internal moulds of brachial valve 



(BB 35349a, b) 12-2 15-5 



External and internal moulds of brachial valve 



(BB 35350a, b) 6-5 7-5 



Incomplete external and internal moulds of 



brachial valve (BB 35351a, b) - - 



Type horizon and localities. Whittery Shales : BB 35343 and 35347 from 

 exposures in the stream at the north end of Spring Coppice, 865 yds south-east of 

 Hockleton Bridge near Chirbury (Grid Ref. SO 279997) '> BB 35350 from exposures 

 in the lower part of the west bank of the River Camlad 60 yds north-east of Marring- 

 ton Farm (Grid Ref. SO 272970) ; all other specimens from Whittery Quarry at 

 the south end of Whittery Wood near Chirbury (Grid Ref. SO 275981). 



Discussion. One Welsh species, Oxoplecia mutabilis Williams (in Whittington & 

 Williams 1955 : 411), and possibly two American forms, the Porterfield 0. gibbosa 

 and the Trenton 0. pennsylvanica (Cooper 1956 : 543, 553) can be assigned to 

 Caeroplecia, although the presence in the two latter species of the ridge-like concentric 

 ornamentation so characteristic of the genus has still to be demonstrated. However, 

 all three differ in the number of ribs on the fold, C. mutabilis having a greater number 

 (6 to 12, usually 9) and the American species significantly fewer (3 or 4) . C. mutabilis, 

 which is probably the most closely related, also differs in being relatively wider and 

 in having grown to lengths of 7 or 8 mm before comparatively fine costae and 

 costellae, with a wavelength of 0-3 to 0-5 mm, appear. 



Table 94 



Statistics of length (1) and maximum width (w) of 7 brachial valves of Caeroplecia plicata gen. et 



sp. nov. 



1 mm (var 1) 9-81 (10-558) 



w mm (var w) 12-31 (17-092) 



r 0-995 



a (var a) 1-2724 (0-00311) 



