ordovician brachiopoda 97 



Table 63 



The distribution of brachial valves of Dalmanella parva Williams (A), D. salopiensis sp. nov. (B), 



D. salopiensis gregaria sp. et subsp. nov. (C) and D. salopiensis transversa sp. et subsp. nov. (D) 



with 4-8 costellae per mm, 2 mm antero-medially of the dorsal umbones 



Costellae per mm 

 45678 

 A 14863 



B 1 11 17 3 - 



C 2 5 9 



D -222- 



Dalmanella elementaria sp. nov. 

 (PL 16, figs. 2-8) 



Diagnosis. Very small, ventribiconvex, sulcate Dalmanella with a finely costel- 

 late ornamentation, faintly impressed bilobed ventral muscle field, slightly divergent 

 dental plates, a short ridge-like cardinal process, subtriangular blade-like brachio- 

 phores with subparallel bases and small fulcral plates. 



Description. Very small, ventribiconvex, subquadrate Dalmanella with rounded, 

 obtuse cardinal angles ; pedicle valve slightly carinate medially, one-third as deep 

 as long ; gently convex brachial valve very rarely more than 3 mm long with a mean 

 length relative to width of 78-3% (variance 109-2) for 5 valves, median sulcus usually 

 persistent, rounded, almost three-fifths as wide as the valve length, bounded by 

 evenly convex lateral areas ; ventral and dorsal interareas short, apsacline and 

 anacline respectively, with an open delthyrium containing a small pedicle callist 

 and an open notothyrium ; ribbing very fine with 7 and 8 costellae per mm, 2 mm 

 antero-medially of the umbones of 5 and 2 brachial valves respectively, first three 

 sectors narrow with simple branching normally consisting of ia, 1, 2a, 2b, 2, 3a!, 3a, 



3, 3a°. 



Teeth supported by slightly divergent dental plates extending forward for an 

 average of 26-3% (variance 46-8) the length of 5 valves ; ventral muscle field rarely 

 and faintly impressed, apparently bilobed, with shorter median adductor scar 

 flanked by lobate diductors. 



Cardinal process consisting of a low impersistent ridge not extending to posterior 

 margin of notothyrium, brachiophores subtriangular, blade-like with subparallel 

 bases extending anteriorly for one-fifth the length of the valve (mean lengths and 

 variances of 13 valves and brachiophore bases = 1-99 (0-256) and 0-41 (0-019) 

 respectively ; r = 0-943) ; sockets narrow, defined by small fulcral plates. 



Type material. 



length width (mm) 

 Holotype External and internal moulds of brachial valve 



(BB 35352a, b) 3-2 3-8 



7 



