ORDOVICIAN BRACHIOPODA 75 



brachiophores supported by short convergent bases, and sockets denned by small 

 fulcral plates. 



These features are consistent with the variability described by Havlicek (1950 : 

 124 ; 1971 : 42) in young specimens of G. partita, although the brachial valve of the 

 Shropshire Gelidorthis appears to be relatively flatter. However only two of these 

 valves are known at present and until more material including adult specimens is 

 available for the significance of this difference to be assessed, there is no justification 

 in according them systematic recognition. 



TAZZARINIA Havlicek 1971 



Tazzarinia elongata sp. nov. 



(PI. 12, figs. 9-12, 15) 



Diagnosis. Elongately subquadrate, ventribiconvex Tazzarinia with a coarsely 

 fascicostellate ornamentation and a dorsal sulcus dying out anteriorly ; bilobed 

 ventral muscle scar extending forward for almost 30% the length of the pedicle 

 valve ; pointed brachiophores supported by short bases. 



Description. Subquadrate, ventribiconvex Tazzarinia with slightly obtuse 

 cardinal angles ; pedicle valve almost as long as wide and one-quarter as deep as 

 long, slightly carinate medially with evenly convex lateral slopes ; brachial valve 

 about four-fifths as long as wide and one-sixth as deep as long, with a narrow median 

 sulcus becoming indistinct beyond the 4 mm growth stage, lateral slopes evenly 

 convex ; radial ornamentation strongly fascicostellate with narrowly rounded 

 costellae numbering 5 per mm, 3-5 mm antero-medially of the dorsal umbo ; ventral 

 interarea slightly curved apsacline, longer than the anacline dorsal interarea, 

 notothyrium and delthyrium open but pedicle callist strongly developed within the 

 latter. 



Teeth supported by narrowly divergent dental plates extending forward for about 

 one-sixth the length of the pedicle valve ; ventral muscle scar strongly bilobed with 

 a median adductor track and flanking diductors impressed anteriorly for almost 

 three-tenths the length of the valve. 



Cardinal process massive with crenulated posterior face, notothyrial platform well 

 developed passing anteriorly into median ridge and flanked by convergent bases of 

 pointed brachiophores, sockets elongate with small fulcral plates ; suboval adductor 

 scars impressed on either side of median ridge and extending anteriorly for over 

 two-fifths the length of the brachial valve. 



Type material. 



length width (mm) 

 Holotype External and internal moulds of brachial valve 



(BB 35332a, b) 5-5 



Paratype External and internal moulds of pedicle valve 



(BB 35333a, b) 3-8 3-8 



