32 SHELVE DISTRICT 



more finely drawn ; and when the internal features of the latter genus become 

 known, it may prove to be a junior synonym of Palaeoglossa. 



Palaeoglossa attenuata (Sowerby) emended A. W. 

 (PI. 3, figs. 2-13) 



1839 Lingula attenuata Sowerby in Murchison : 641. 

 1866 Lingula attenuata Sowerby ; Davidson : 44. 



Diagnosis. Subequally biconvex Palaeoglossa with a brachial valve 73% as 

 wide and 6% as deep as long and a pedicle valve 71% as wide and 7% as deep as 

 long ; fila fine and discontinuous ; ventral pseudointerarea with a shallow narrow 

 pedicle groove extending anteriorly for 11% of the length of the pedicle valve, and a 

 dorsal pseudointerarea and low median ridge extending forward for 7% and 43% 

 of the brachial valve length respectively. 



Description. Subequally biconvex, elongately oval Palaeoglossa with curved 

 lateral and rounded anterior margins, brachial valve 73% as wide as long and 6% as 

 deep as long (with a range of 3% to 8% for 9 valves), pedicle valve 71% as wide as 

 long and 7% as deep as long, both valves evenly convex in longitudinal and trans- 

 verse profiles ; external surface ornamented by growth lines and fine discontinuous 

 fila about 0-25 mm in wavelength ; ventral beak acutely incurved, dorsal beak 

 obtusely rounded. 



Ventral pseudointerarea striated, slightly anacline, crescentic in outline, 11% as 

 long medially as the length of the valve, pedicle trough narrow and shallow ; divided 

 umbonal muscle scars rarely impressed. 



Dorsal pseudointerarea striated, almost orthocline, lenticular in outline and 

 extending forward medially for 7% of the length of the valve (range 6% to 8% for 6 

 specimens) ; divided umbonal muscle scars rarely impressed on either side of a low 

 variably developed median ridge extending anteriorly for 43% of the length of the 

 valve (range 28% to 66% for 5 specimens). 



Figured material. 



External and internal moulds of brachial valve (BB 37109a, b) 



External and internal moulds of pedicle valve (BB 37110a, b) 



External and internal moulds of pedicle valve (BB 37111a, b) 



Exterior of pedicle valve (BB 37112) 



Exterior of pedicle valve (BB 37113) 



External and internal moulds of brachial valve (BB 37114a, b) 



Internal mould of pedicle valve (BB 37115) 



External and internal moulds of pedicle valve (BB 37116a, b) 



External and internal moulds of disarticulated valves 



(BB 37117a, b) 



External and internal moulds of brachial valve (BB 37118a, b) 



Horizons and localities. Meadowtown Beds : BB 37111, 37114 from outcrops 

 on the Meadowtown -Rorrington road, 220 yds from Meadowtown Chapel (Grid Ref. 



sngth 



width (mm) 



11-0 



8-0 



7-0 



5-0 



12-5 



87 



8-3 



6-o 



6-5 



4-5 



13-0 



9-0 



16-0 



- 



5-5 



3-6 



55 



3-o 



12-0 



9-0 



