154 SHELVE DISTRICT 



Horizon and locality. Spy Wood Grit exposed noo yds NNE of Rorrington 

 (GridRef. S J 303015). 



Discussion. Rostricellula is rare in the Shelve area, being represented only by a 

 few valves from the Spy Wood Grit which are quite different in ornamentation and 

 outline from all other described species except R. sparsa from the Allt Ddu Mud- 

 stones of the Bala district. In every morphological aspect the Spy Wood specimens 

 are identical with the small sample on which the Welsh species was based. Especially 

 significant for immediate identification is the presence of 2 costae on the fold. Only 

 one American and one European species are known with so few ribs. They are : 

 R. ? minuta from the Hermitage Formation of Tennessee which, although similar in 

 shape, has 7 or 8 costae on each lateral slope (Cooper 1956 : 640) ; and R. ambigena 

 (Barrande) from the Upper Ordovician of Bohemia (Havlicek 1961 : 51) which is not 

 only relatively longer but has the costae on the fold and sulcus branching within the 

 size range of the British species. 



Order SPIRIFERIDA Waagen 1883 



Suborder ATRYPIDINA Moore 1952 



Superfamily ATRYPACEA Gill 1871 



Family ATRYPIDAE Gill 1871 



Subfamily ZYGOSPIRINAE Waagen 1883 



ZYGOSPIRA Hall 1862 



Zygospira sp. 



(PI. 27, figs. 12, 13) 



An internal mould (BB 37133) has been recovered from Spy Wood Grit outcrops 

 1 100 yds NNE of Rorrington (Grid Ref. SJ 303015), which is likely to represent the 

 remains of a brachial valve of the atrypacean Zygospira. The rostrate valve, which 

 was about 2 mm long, was nearly circular in outline and about 15% as deep with a 

 shallow narrow median sulcus and evenly convex lateral areas. The external surface 

 was ornamented by about 15 fine costae while internally a median ridge corresponding 

 to the narrow sulcus supported a divided hinge plate with rounded crural bases. 



This occurrence is one of the earliest records of Zygospira, which has hitherto 

 been described from younger Ordovician strata in N. America (Cooper 1956 : 672- 

 674), Scotland (Williams 1962 : 242) and Mid-Europe (Havlicek & Vanek 1966 : 61). 

 The relatively few ribs may be diagnostic but may also reflect immaturity of the 

 specimen and detailed comparison with established species would not be profitable 

 at present. 



VI. ACKNOWLEDGMENTS 



This systematic survey could not possibly have been undertaken without the active 

 encouragement of the late Professor W. F. Whittard, F.R.S. who so generously put 

 his unique collection of Shelve brachiopods at my disposal and indeed sponsored 



