Generic placement

MASSE, JEAN-PIERRE, FENERCI-MASSE, MUKERREM & BUCUR, IOAN I., 2024, New Species Of The Lower Cretaceous Genus Matheronia Munier-Chalmas (Bivalve Hippuritida) In Romania, Acta Palaeontologica Romaniae 20 (1), pp. 3-15 : 10

Generic placement . The RV myophores are represented by an anterior, low, protruding internal bulge ( Fig. 6a, b ) and a posterior, cross-sectional triangular marginal crest. LV myophores are on shell wall. This organisation is typical of Matheronia .

Specific assignment. LV myophores on shell wall, absence of radial bands on the posterior side of the LV, its short beak and the uncoiled RV are common attributes of the genus Matheronia . The overall transverse outline is subtriangular with an antero-posterior compression ( Fig. 6a, b ). Concentric growth lines issued from the dorsal side are characteristic features of the flat RV which ends by a ventral blunt carina ( Fig. 6d ). The LV has a lamellar, thick (up to 5 mm) concave anterior side, and a thin (about 1 mm) convex smooth or irregular posterior side. The carina is acute ( Fig. 6c ) asymmetric; it tends to slightly override the anterior shell side ( Fig. 6e ). Average dimensions and ranges are as follows: Dap = 30 mm (2.5 - 40 mm), Ddv = 27 mm (20-32 mm); RV length = 60 mm (55-65 mm), LV length= 35 mm.

Diagnosis. Matheronia with a medium size, toucasiform,

i.e. with an antero-posterior compression, LV anterior side concave, with an acute ventral carina.

Comparisons. The size of Matheronia carinata sp. nov. is in the range of that of M. aptiensis , i.e. smaller than M. munieri and M. virginiae . It also differs from the West European species by a more concave LV anterior side and a more acute carina. The radial bands of M. carinata sp. nov. are inconspicuous, hence different from that of Matheronia baksanensis and M. aptiensis , somewhat outlined. Due to its antero-posterior compression coupled with the acute carina, M. carinata sp. nov. looks like Toucasia , it is the only toucasiform Matheronia species known so far. Dap is larger than Ddv, two dimensions nearly equivalent in M. aptiensis .

Figures

Fig. 6. Matheronia carinata sp. nov. from Valea Minişului. a. Transverse section showing the myophoral organisation (specimen IB 5443-1, holotype), specimen partly damaged, almost shell free. b. ibidem, reconstitution. c. ibidem, ventral view of the LV showing the acute ventral carina (ca). d. External view of RV with concentric growth lines (specimen IB 5443-3). e. Anterior view of a LV showing the acute carina (ca) slightly overriding the anterior shell side (specimen IB 5443-2). Scale bar 10 mm.