ORDOVICIAN BRACHIOPODA 143 



length width (mm) 

 External and internal moulds of brachial valve 

 (BB 35563a, b) io-o n-5 



External and internal moulds of brachial valve 

 (BB 35564a, b) 7-5 9-0 



Horizon and localities. Meadowtown Beds : BB 35558 and BB 35564 from 

 exposures 100 yds south-east of Minicop Farm (Grid Ref. SJ 315018) ; all other 

 specimens from Quinton's Quarry in a field 200 yds north-east of Meadowtown 

 Chapel (Grid Ref. SJ 312013). 



Discussion. The Rafinesquina found sporadically in the Betton Beds and 

 occurring abundantly in the Meadowtown Beds (Tables 105-110) is especially 

 characterized by the delicacy of its cardinalia, the weakness of its notothyrial plat- 

 form and the smallness of its subcircular ventral muscle scar. Indeed if it were not 

 for the presence of strongly developed dental plates, the species would have been 

 more appropriately classified as Platymena (Cooper 1956 : 879). The nature of these 

 features also serves to distinguish the new species from its closest relative, the Upper 

 Llandeilo R. simplex (MacGregor 1961 : 205) which, in particular, has a better defined 

 notothyrial platform and significantly larger ventral muscle scar. In the absence 

 of statistical data from MacGregor' s account of R. simplex, no other difference may 

 be categorically identified at present, although the brachial valve of the Welsh 

 species may prove to be relatively wider than that of R. delicata. 



Rafinesquina sp. 



(PL 25, fig. 1 ; PL 26, fig. 1) 



The only specimens from the Whittery Shales referrable to Rafinesquina are 

 incomplete complementary external and internal moulds of a brachial valve 

 (BB 35496a, b) recovered from Whittery Quarry at the south end of Whittery Wood, 

 near Chirbury (Grid Ref. SO 275981). The valve was gently concave with a promi- 

 nent protegulum about 0-5 mm long and an unequally parvicostellate radial 

 ornamentation with a density of 10 ribs per mm antero-medially of the umbo. 

 Impersistent rugae up to 2 mm in wavelength were developed in arcs concentric to 

 the umbo and immediately distinguish the specimen from the Meadowtown Rafines- 

 quina. Internally the cardinal process lobes were ridge-like and slightly divergent 

 and capped postero-medially by a strong chilidium. The socket ridges were narrow 

 and low and the anchor-shaped notothyrial platform weakly developed with only 

 one pair of transmuscle septa evident. 



A number of strophomenids have been recorded from the Caradocian rocks of 

 England and Wales as Rafinesquina expansa (Sowerby) but the species requires 

 revision because, as currently understood (Davidson 1871 : 312), it includes specimens 

 that are not even congeneric ; and until more material is available no comparisons 

 are trustworthy. 



