102 shelve district 



Table 72 



Statistics of length (1) of n brachial valves and length of adductor scars (sc) of Onniella ostentata 

 lepida subsp. nov. from the Aldress Shales (A) and Whittery Shales (B) 



A B 



n 15 10 



1 mm (var 1) 3-2 (0-696) 4-27 (1-438) 



s"c mm (var sc) 1-88 (0-235) 2-3 (0-4) 



r 0-833 o-979 



a (var a) 0-581 (0-00794) 0-5274 (0-00146) 



Family HARKNESSELLIDAE Bancroft 1928 

 HARKNESSELLA Reed 1917 

 Harknessella cf. subplicata Bancroft 

 (PL 16, fig. 16) 



An incomplete internal mould (BB 35427), about 3 mm long, from the Spy Wood 

 Grit exposed on top of the ridge 1440 yds NNE of Rorrington bench mark 599 

 (Grid Ref. SJ 303018), appears to represent the immature brachial valve of a 

 Harknessella. The semi-oval valve was about three-fifths as long as wide and almost 

 one-fifth as deep as long with a well-developed median sulcus over half as wide as the 

 valve length and gently convex lateral areas. Ribbing impressions on the mould 

 reach almost to the cardinalia and suggest a coarsely costellate arrangement with 

 about 4 per mm towards the anterior margin. The cardinalia consisted of a cardinal 

 process differentiated into a stout shaft and crenulated myophore, obliquely disposed 

 sockets defined by fulcral plates and brachiophores supported by acutely divergent 

 bases indented submedially by deep adductor pits. 



The development of adductor pits and the disposition of the brachiophore bases 

 and fulcral plates to give the 'angulated subparallel pre-socket lines' of Bancroft 

 (1945 : 225) indicate that the brachial valve belonged to Harknessella ; the relative 

 coarseness of the ribbing further suggests its close affinities with the species H. 

 subplicata Bancroft (1945 : 226) from the Coston Sandstone of E. Shropshire. 



HORDERLEYELLA Bancroft 1928 



Horderleyella cf. plicata Bancroft 



(PL 16, figs. 17, 19, 20 ; PL 17, fig. 1) 



Diagnosis. Small, subquadrate Horderleyella ornamented by 3 to 5 fasci- 

 costellae per mm, 2 mm antero-medially of the dorsal umbo ; bilobed ventral 

 muscle scar extending anteriorly for about two-fifths the valve length ; cardinal 

 process blade-like, subparallel brachiophores extending forward for about 12% of 

 the valve length and dorsal adductor scars impressed posteriorly in shallow hollows 

 in the notothyrial platform. 



Description. Small, subquadrate, ventribiconvex Horderleyella with cardinal 

 angles approximating to 90 ° ; pedicle valve carinate medially, 30% as deep as long ; 



