Annals of the South African Museum

angles anterior anteroventrally appearance beaks become broad coarse comprises concave concentric conocardiiformis Krauss convex Cooper crenulated Cretaceous crowded curved Description designation Diagnosis differs Discussion dorsal elongate escutcheon face faunas figured fine finely flank costae follow Formation genus groove growth rugae Hoepen holotype holubi Kitchin included inflated anteriorly interspaces Iotrigonia irregular Kitchin Kobayashi Lateral view left valve length longitudinal marginal carina material maturity maximum meet Megatrigonia moderately Myophorella Nakano narrow Neocomian nepionic stages nodate nodes Note oblique obsolete Occurrence opisthogyrous original ornament persists Port Elizabeth Museum posterior posteriorly primitive Pringle produced prominent Pterotrigonia radial references region respiratory margin restricted Reyes ribs rounded rows separates Sharpe shell shoulder similar Skwarko slightly smooth South African Museum species specimens Steinmanella straight strongly subconcentric subfamily Superfamily Tashiro transverse transverse costellae Trigonia Trigoniinae tubercles Type umbones Upper V-shaped Valanginian valve ventral margin weakly