82 SHELVE DISTRICT 



Family SKENIDIIDAE Kozlowski 1929 



Genus SKENIDIOIDES Schuchert & Cooper 1931 



Skenidioides cf. costatus Cooper 



(PI. 13, figs. 14-16 ; PI. 14, figs. 1-3) 



1956 Skenidioides costatus Cooper : 493. 



1963 Skenidioides cf. costatus Cooper; Williams : 375. 



Diagnosis. Subpyramidal, ventribiconvex Skenidioides with a carinate pedicle 

 valve 54% as long as wide and 55% as deep as long, ornamented by up to 8 costae 

 on each of the lateral slopes and a thick median costa giving rise to a pair of lateral 

 costellae 1*5 mm anterior of the umbo. 



Description. Semi-oval, sulcate Skenidioides with a subpyramidal, carinate 

 pedicle valve with a mean length relative to width of 54% (range 50% to 59%) for 

 4 valves and a mean depth relative to length of 55% (range 53% to 58%) for 3 valves ; 

 brachial valve very gently convex with a sharp median sulcus ; radial ornamentation 

 costate with up to 8 rounded costae occupying each lateral slope but with ventral 

 carina defined by thick rounded costa, about 0-5 mm in wavelength 2 mm anterior 

 of ventral umbo, giving rise to a pair of lateral costellae about 1-5 mm anterior of 

 ventral umbo. 



Ventral interior with free spondylium about one-fifth as deep as the length of the 

 valve. 



Dorsal interior with thin and plate-like cardinal process continuous with high 

 median septum, brachiophore bases converging onto dorsal septum at an average of 

 33% the length of 2 brachial valves ; dorsal adductor field as a pair of subtriangular 

 impressions divided by median septum and extending anteriorly for nearly three- 

 fifths the length of the brachial valve. 



Figured material. 



length width (mm) 



Internal mould of brachial valve (BB 35409) 2-3 4-4 



Incomplete internal mould of pedicle valve (BB 35410) 2-5 4-4 



Internal mould of pedicle valve (BB 3541 1) 1-2 27 



Internal mould of pedicle valve (BB 35412) 0-8 1-5 



Incomplete external mould of pedicle valve (BB 35413) 1*5 - 



Horizons and localities. Spy Wood Grit : BB 35411 to 35413 from exposures 

 in north bank of Spy Wood Brook, 170 yds north-east of Spy Wood Cottage 

 (Grid Ref. SO 282958). Whittery Shales : BB 35409 from exposures in the lower 

 part of the west bank of the River Camlad, 60 yds north-east of Marrington Farm 

 (Grid Ref. SO 272970) ; BB 35410 from exposures in the stream at the north end 

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



Discussion. Moulds of Skenidioides occur only rarely in both the Spy Wood 

 Grit and Whittery Shales but are clearly related to the species found in the Gelli-grin 



