28 SHELVE DISTRICT 



Horizon and locality. All specimens from Stapeley Shales exposed in Whits- 

 burn Dingle 650 yds WSW of Lord's Stone, Leagh (Grid Ref. SJ 328019). 



Discussion. Subcircular inarticulates, occurring fairly abundantly in the Stape- 

 ley Shales and the Meadowtown and Rorrington Beds, are provisionally assigned to 

 the obolid genus Schmidtites only because of the lack of muscle platforms which are 

 normally elaborate structures in other obolinids. With regard to the modest differ- 

 entiation of the posterior margins, here interpreted as poorly developed pseudo- 

 interareas, the new species differs even from other described Schmidtites, and may 

 eventually prove to be generically separable from all other lingulaceans, to which 

 superfamily it almost certainly belongs. 



Notwithstanding the obscurity of internal features and simplicity of shape, the 

 conspecific Meadowtown and Rorrington samples are significantly different 

 (p < 0-02) from specimens recovered from the Stapeley Shales which became pro- 

 gressively longer than wide during growth (Table 12). The difference has been 

 recognized by the erection of a new subspecies. 



Table 12 



Statistics of length (1) and maximum depth (w) of n pedicle valves of Schmidtites ? simplex sp. nov. 



from the Rorrington Beds (A) and the Meadowtown Beds (B), and of Schmidtites ? simplex 



subcircularis sp. et subsp. nov. from the Stapeley Shales (C) 





A 



B 



C 



n 



29 



20 



9 



1 mm (var 1) 



2-88 (1-148) 



2-98 (1-235) 



3-13 (3-23) 



w mm (var w) 



2-9(1-145) 



3-01 (1-244) 



3-00 (1-952) 



r 



o-995 



0-977 



0-986 



logel (var logel) 



0-9927 (0-1296) 



1-0288 (0-1296) 



o-i (0-2844) 



log e w (var log e w) 



0-9996 (0-1279) 



1-0358 (0-129) 



1-0004 (°' I 9°3) 



r e 



o-995 



0-979 



099 



a (var a) 



0-9931 (0-00037) 



Q-9975 (0-00231) 



0-8307 (0-00195) 



Subfamily LINGULELLINAE Schuchert 1893 



LINGULELLA Salter 1866 



Lingulella displosa sp. nov. 

 (PI. 2, figs. 2-8) 



Diagnosis. Ventribiconvex, elongately oval to subtriangular Lingulella with a 

 brachial valve 87% as wide as long and a pedicle valve up to 13% as deep as long, 

 ornamented by impersistent concentrically arranged lamellae, pedicle groove and 

 dorsal pseudointerarea extending anteriorly for 9% and 7% to the valve length 

 respectively. 



Description. Ventribiconvex Lingulella normally changing in outline from 

 elongately oval to subtriangular with a broadly rounded to truncated anterior margin 

 by an acceleration in antero-lateral shell accretion during adult growth stages ; 

 brachial valve 87% as wide and less than 10% as deep as long, pedicle valve about 

 13% as deep as long and 87% as wide as long (range 77% to 97% for 6 specimens), 



