ORDOVICIAN BRACHIOPODA 117 



European and African species, such as T. simplex from the Ktaoua Formation of 

 Morocco (Havlicek 1971 : 66) and T. deformata (Barrande 1879) from the Zahofany 

 Formation of Czechoslovakia (Havlicek 1950 : 89), with their gently rounded non- 

 geniculate sulci. It is, however, similar to T. subcarinata (Cooper 1956 : 538) from 

 the Lebanon Formation of Tennessee ; but systematic consideration of this apparent 

 relationship must await the information provided by more material. 



BICUSPINA Havlicek 1950 



Bicuspina subquadrata sp. nov. 



(PI. 19, figs. 17-19 ; PL 20, figs. 1, 2) 



Diagnosis. Subquadrate Bicuspina, with a dorsal fold about 44% as wide as the 

 brachial valve length, usually bearing a median costa which rarely branches within 

 5 mm of the umbo, finely lamellose with 7 lamellae developed between 5 and 6 mm 

 antero-medially of the umbo. 



Description. Medium-sized, dorsibiconvex, subquadrate Bicuspina with 

 rounded, obtuse cardinal angles ; pedicle valve 25% as deep as long with flat- 

 bottomed median sulcus bounded by parallel sides and evenly convex flanks ; brachial 

 valve 65% as long as wide and 37% as deep as long with a strong median fold 44% 

 as wide as the valve is long ; ventral interarea curved apsacline, pseudodeltidium 

 with narrow median fold, dorsal interarea vestigial ; radial ornamentation of 

 rounded ribs with a mean wavelength of 0-44 mm (variance 0-02), 5 mm anterior of 

 the umbones of 15 brachial valves — a median costa (flanked by 2 laterals) occurs on 

 folds of 11 out of 16 brachial valves and bifurcates within 5 mm of the umbo in 

 only 1 valve — 9 to 15 ribs occur on the flanks of brachial valves between 5 and 

 7-5 mm long ; concentric ornamentation of delicate overlapping lamellae with 6 or 

 7 occurring between 5 and 6 mm anteriorly of the umbones of 2 and 7 brachial valves 

 respectively. 



Pedicle tube relatively short, averaging 12% the length of the pedicle valve and 

 with slightly curved pedicle passage ; rounded teeth supported by acutely divergent 

 dental plates 60% as long as their anterior separation and extending forward for 

 17% of the length of the valve ; suboval muscle field well impressed in late adult 

 stages of growth only, extending forward for 48% of the length of the pedicle valve 

 and consisting of a short median adductor and a pair of ventral adjustors situated 

 on either side of the internal opening of the pedicle tube, which is flanked by long 

 diductor scars. 



Cardinalia consisting of forked, posteriorly curving cardinal process, and short, 

 acutely divergent, pointed brachiophores ; sockets disposed parallel to the hinge-line, 

 extending laterally for 33% of the length of the valve, not restricted distally by 

 ridges of secondary shell. 



Type material. 



length width (mm) 

 Holotype Internal and incomplete external moulds of 



pedicle valve (BB 35480a, b) 18-0 20-0 



