ordovician brachiopoda 145 



Table iio 



Statistics of length (1) and width (w) of the ventral muscle scar in 23 pedicle valves of Rafinesquina 



delicata sp. nov. 



Imm(varl) 3-6 (1-351) 



w mm (var w) 3-56 (1-107) 



r 0-96 



a (var a) 0-9052 (0-00302) 



KJAERINA (HEDSTROEMINA) Bancroft 1929 

 Kjaerina (Hedstroemina) sp. 



(PI. 26, fig. 2) 



The internal mould of a pedicle valve (BB 35452) from the Spy Wood Grit cropping 

 out 1 100 yds NNE of Rorrington (Grid Ref. SJ 303015) will probably be shown to 

 represent a new species of the Kjaerina species group known as Hedstroemina 

 (Bancroft 1929 : 56). The convex valve was about 20 mm long and an estimated 

 30 mm wide with roundly obtuse cardinal angles affected by a strong but sharply 

 obtuse geniculation to define a relatively flat disc about 10-5 mm long and a trail 

 15 mm long. Fragments of the external mould at the antero-medial margin 

 indicated that the radial ornamentation was coarsely unequally parvicostellate with 

 about 4 ribs per mm. The ventral interarea was strongly apsacline, the foramen 

 large and supra-apical with a small or resorbed pseudodeltidium. The well-developed 

 teeth were supported by divergent dental plates subtending an angle of about ioo° 

 and extending forward for about 15% of the length of the disc. Low convergent 

 ridges extended from the anterior ends of the dental plates to enclose a subcircular 

 muscle field about 70% as long as the disc with a broad median adductor scar extend- 

 ing anteriorly as far as the subflabellate diductor impressions. 



The specimen is quite distinct from other known Hedstroemina in the strong 

 geniculation of the valve and the large size of the scar in relation to the disc. The 

 Actonian H. robusta (Bancroft 1929 : 59) and H. holtedahli (Spjeldnaes 1957 : 131) 

 from the 4ba-/? horizons of Norway compare most closely, but neither is so sharply 

 deflected nor characterized by so small a disc. 



Subfamily GLYPTOMENINAE Williams 1965 

 BYSTROMENA gen. nov. 



Name. A strophomenacean with the posterior of the adult pedicle valve blocked 

 by a plug (Gk. flvoTpa). 



Diagnosis. Concavo-convex, semi-elliptical strophomenids with large protegula, 

 ornamented by parvicostellae which may be unequaUy developed in early growth 

 stages ; ventral and dorsal interareas apsacline and anacline respectively, pseudo- 

 deltidium bounding a large supra-apical foramen truncating the ventral beak, 

 arched chilidium relatively large. 



