ORDOVICIAN BRACHIOPODA 



129 



vascula media and terminal branches but possibly associated as a pinnate pattern 

 with low thin ridges radiating from vicinity of delthyrial cavity. 



Dorsal interior with flattened, slightly indented ventral ends of chilidial plates 

 filling notothyrial cavity and continuous with slightly convex plate-like socket 

 ridges disposed parallel to hinge-line ; notothyrial platform absent so that cardinalia 

 overhang a shallow posteromedian depression passing anteriorly into low narrow 

 median ridge ; adductor muscle field quadripartite bounded by outwardly curving 

 raised ridges ; dorsal mantle canal pattern preserved only peripherally, possibly 

 pinnate. 



Type species. Eocramatia dissimulata sp. nov. from the Hope Shales. 



Eocramatia dissimulata sp. nov. 

 (PI. 21, figs. 9, 12, 14, 15 ; PI. 22, figs. 1-3, 5, 6 ; Text-fig. 10) 



Diagnosis. Subquadrate, uniplicate, plano-convex Eocramatia with the pedicle 

 valve 74% as long as wide and 18% as deep as long and ornamented by costellae 

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

 scars limited to the posterior half of the valve. 



Description. Subquadrate, plano-convex Eocramatia with 3 pedicle valves 

 averaging 74% as long as wide (range 68% to 81%) and 18% as deep as long (range 

 17% to 19%) bearing a shallow median sulcus less than one-third as wide as the 

 hinge-line and a brachial valve nearly three-fifths as long as wide bearing a vague 

 median fold, cardinal margins acute ; costellate ornamentation fine, numbering 

 5 per mm, 5 mm antero-medially of the umbones of 3 pedicle valves ; apsacline 

 ventral interarea 19% as long as the pedicle valve (average for 4 valves, with a range 

 of 15% to 22%) with the pseudodeltidium extending forward for about one-seventh 

 the length of valve, hypercline dorsal interarea shorter. 



foramen 



chilidial plate C) 



socket ridge 

 tooth 



muscle scar 



A B 



Fig. 10. Diagrammatic views of (A) the ventral interior and (B) the dorsal interior, 

 with a posterior view of the brachial valve above, of Eocramatia. 



