Promyalina schamarae ( Bittner, 1899 )

Foster, William J., Danise, Silvia & Twitchett, Richard J., 2017, A silicified Early Triassic marine assemblage from Svalbard, Journal of Systematic Palaeontology 15 (10), pp. 851-877 : 854-855

Promyalina schamarae ( Bittner, 1899)

( Fig. 2C–G )

1899 Myalina schamarae Bittner 19, pl. 4, figs 20–25.

2009 Promyalina schamarae (Bittner) ; Kumagae & Nakazawa: 157, fig. 144, 4–5.

Material. Three specimens from LD-04 ( NHMUK PE PEI 5484 ; NHMUK PI MB 1202 ; NHMUK PI MB 1205 ) and seven specimens from LD-05 ( NHMUK PI MB 1188 ; NHMUK PI MB 1203–1204 ; NHMUK PE PEI 5475– 5476; NHMUK PE PEI 5500; NHMUK PE PEI 5503) .

Description. Shell is small, mytiliform, inequilateral, prosocline, higher than long, and moderately inflated. Umbo is small, terminal and prosogyrate. Posterior dorsal margin is straight. Posterior margin is slightly convex, forming a rounded posteroventral margin. Anterior margin is long, nearly straight or weakly acute and partly depressed near the umbo.

Remarks. The internal characters of the shells cannot be observed because all the specimens are articulated. Externally, the shells resemble Promyalina schamarae from the Griesbachian Lazurnaya Bay Formation, Russia (Shigeta et al. 2009), and are therefore assigned to this species. These specimens differ from P. groenlandica ( Newell, 1955) , as the beak does not project beyond the dorsal margin, and from P. spathi in having a more convex anterior margin.

Mode of life. Surficial, stationary, attached, suspension feeder (Stanley 1972).

Figures

Figure 2. A, Orbiculoidea winsnesi Gobbet, 1963, NHMUK PI BE 3238, dorsal view, dorsal valve; B, Austrotindaria? canalensis (Catullo, 1846), NHMUK PI MB 1198, external view, left valve; C–G, Promyalina schamarae (Bittner, 1899), external view; C, D, NHMUK PI MB 1204; C, right valve; D, left valve. E, F, NHMUK PI MB 1203; E, right valve; F, left valve. G, NHMUK PI MB 1202, right valve. Scale bars: A, B, G = 2 mm, C–F = 1 mm.