ORDOVICIAN BRACHIOPODA 47 



Family DISCINIDAE Gray 1840 



Subfamily ORBICULOIDEINAE Schuchert & Le Vene 1929 



ORBICULOIDEA d'Orbigny 1847 



Orbiculoidea sp. 



(PL 7, fig. 1) 



An external mould with adherent shell of a brachial valve of Orbiculoidea (BB 35576) 

 has been recovered from an unlocated exposure of Stapeley Shales. The valve 

 which was 7 mm long and 1-2 mm deep was subcircular in outline with the beak 

 situated about 2-5 mm forward of the slightly truncated posterior margin. The 

 posterior sector was slightly concave, but the rest of the valve sloped evenly away 

 from the beak to a flattened margin about 0-5 mm wide. The external surface was 

 ornamented by fine fila ; no internal features are known. 



No useful purpose is served in comparing this brachial valve with those of 

 described species, many of which are similarly proportioned. The specimen however 

 constitutes an interesting record as one of the earliest Orbiculoidea so far identified. 



SCHIZOTRETA Kutorga 1848 



Schizotreta transversa sp. nov. 



(PI. 7, figs. 2, 3, 7) 



Diagnosis. Subcircular Schizotreta slightly wider than long with a ventral beak 

 located one-third of the valve length forward of the posterior margin and a surface 

 ornament consisting solely of growth lines. 



Description. Subcircular Schizotreta with a slightly truncated posterior margin, 

 brachial valve very gently convex, pedicle valve subcorneal, almost nine-tenths as 

 long as wide and just over one-fifth as deep as long, with an even slope away from 

 the beak except for a slightly concave posterior margin and immediately in front of 

 the slit -like pedicle opening ; dorsal beak submarginally located just over one-tenth 

 forward of the posterior margin ; surface of both valves ornamented solely by fine 

 growth fines ; interiors unknown. 



Type material. 



length width (mm) 



Holotype Exfoliated pedicle valve (BB 35577) 27 3-1 



Paratypes Exfoliated pedicle valve (BB 35578) 4-5 5-0 



Exfoliated brachial valve (BB 35579) 4-5 - 



Type horizon and localities. Meadowtown Beds : BB 35577, 35578 from 

 exposures 80 yds from Meadowtown Quarry along the Rorrington road (Grid Ref . 

 SJ 311012). BB 35579 from exposure in lane to Kinton, 200 yds west of Holy 

 Trinity Church, Middleton (Grid Ref. SO 295993). 



Discussion. There seems to be little doubt that the discinid specimens collected 

 from the Meadowtown Beds, and also a few less well-preserved moulds from the 

 Rorrington Beds, should be assigned to Schizotreta because the beak of the brachial 



