Two new Late Triassic nuculanoidean bivalve genera from north-west Yunnan, China

The two new nuculanoidean bivalve genera Yongshengia n. gen. and Ningliconcha n. gen. with the type species Yongshengia cuneata (CHEN, in MA et al. 1976) and Ningliconcha ningliensis n. gen. n. sp. from Norian (Late Triassic) strata of north-west Yunnan Province, south-west China, both exhibit unusual morphologic features. Yongshengia is one of the largest nuculanoideans known and somewhat tentatively included into the Malletiidae. The new genus is further characterised by ( I) a small resilifer, which is only present in right valves of adult growth stages and lacking in juvenile shells, (2) a shell Sculpture consisting of two orders of commarginals and very weak radials, and (3) a particularly large posterior pedal retractor Muscle sear. Ningliconcha is a small- to medium-sized malletiid with subtrigonal to subtrapezoidal shell shape and cancellate shell sculpture.