ORDOVICIAN BRACHIOPODA 49 



Interior of brachial valve with strongly impressed suboval postero-lateral adductor 

 scars smaller than suboval elevated anterior adductor scars situated submedially 

 up to 60% forward of the posterior margin and ornamented by fine parallel wavy 

 ridges ; mantle canal system pinnate with variably impressed sigmoidal vascula 

 later alia. 



Type material. 



length width (mm) 

 Holotype External and internal moulds of brachial valve 



(BB 35405a, b) n-5 14-0 



Horizon and locality. Whittery Shales : exposures in stream at north end of 

 Spring Coppice 865 yds south-east of Hockleton Bridge (Grid Ref. SO 279997). 



Discussion. Although the sole craniid found in the Shelve area is represented by 

 only 4 adult brachial valves from the Whittery Shales and a single immature brachial 

 valve from the Aldress Shales, it is distinctive enough to be recognized as a new 

 species. Its smooth slightly irregular external appearance suggests that it is best 

 assigned to Petrocrania and the sigmoidal vascula lateralia impressed on the internal 

 surface confirm this allocation. There are, however, two other internal features which 

 are not typical of Petrocrania. They are the greater size of the anterior adductor 

 scars compared with the posterior pair and the thickened margin. The new species, 

 therefore, differs from other described Petrocrania in these characters. It is also 

 distinctive in the mid-region location of the valve beak which is situated much nearer 

 the posterior margin in American species of Ordovician age (Cooper 1956 : 287-291) 

 and in P. inexpectata (Barrande 1848 : pi. no, fig. V) from the Caradocian Zahofany 

 Formation of Czechoslovakia. 



Class ARTICULATA Huxley 1869 



Order ORTHIDA Schuchert & Cooper 1932 



Suborder ORTHIDINA Schuchert & Cooper 1932 



Superfamily ORTHACEA Woodward 1852 



Family HESPERONOMIIDAE Ulrich & Cooper 1936 



HESPERONOMIA Ulrich & Cooper 1936 



Hesperonomia sp. 



(PL 7, figs. 9, 12) 



The slightly deformed external and internal moulds (BB 35334a, b) of a brachial 

 valve, collected from the Mytton Flags exposed between 50 and 55 yds down the 

 lane from Woodside House (Grid Ref. SJ 337002), are representative of the genus 

 Hesperonomia Ulrich & Cooper. The subquadrate gently concave valve was about 

 7 mm long and had an anacline interarea about one-seventh as long as the valve, 

 and an open notothyrium. The ornamentation consisted of fine costellae, arising by 

 intercalation with a density of 6 per mm, 5 mm antero-medially of the umbo, and 

 segregated into narrow sectors by a thickening of every eighth to tenth rib. In- 

 ternally a blade-like cardinal process was supported on a low notothyrial platform 



