Type species. Venericardia tehuelchana Ihering, 1907 (pl. 16, figs 107a–b). Surroundings of Cerro Laciar (Feruglio 1954), lower Pliocene, Santa Cruz, Argentina.
Diagnosis. Carditid with small (less than 30 mm in length) and high shell with subtriangular outline and a convex dorsal margin. Left anterior tooth large and vertical, right middle tooth small and slightly inclined posteriorly. External sculpture of 9 to 15 low, smooth and flat radial ribs, widening towards the central region of the valve with wide intercostal spaces.
Included species. Venericardia (Pleuromeris) marshalli Marwick, 1924 (upper Pliocene–Recent, Petane Clays, New Zealand), Pleuromeris murdochi Powell, 1938 (upper Pliocene, Castle Point, New Zealand), Pleuromeris paucicostata Laws, 1940 (upper Pliocene–Recent, Nukumaru, New Zealand).
Derivation of name. From ‘ kol ’ (Aonikenk, original language of the Aonikenk or Tehuelche’s people, early inhabitants of Santa Cruz Province) that means ‘seashell’, and ‘- meris ’, a common suffix employed for small carditids and which probably comes from Latin word ‘ maris ’ that means ‘from the sea’.
Remarks. Kolmeris n. gen. shares characters with Pleuromeris and Pteromeris Conrad, 1862 (type species Cardita perplana Conrad, 1841; Pliocene–Recent of North Atlantic Ocean) (Gardner 1943: pl. 13, figs 6–9) such as their small and subtriangular shell, pointed umbo, large lunule, right middle tooth being triangular and vertical and a sculpture of usually less than 20 wide radial ribs.
The new genus can be separated from Pleuromeris by having a higher shell with convex dorsal margin, less pointed umbo, a larger right anterior tooth and fewer, lower and wider radial ribs not covered by nodes. It can be distinguished from Pteromeris by the absence of the typical recurved and anteriorly directed umbo that characterizes this genus, the presence of a smaller right middle tooth and straight left posterior tooth, and by the development of wider intercostal spaces.
Kolmeris differs from Coripia de Gregorio, 1885 (type species Cardita unidentata Basterot, 1825; Pliocene– Recent of Northeast Atlantic Ocean and Mediterranean Sea) (Pras 2013: pl. 1, figs 4–7) and Miodontiscus Dall, 1903 (type species Miodon prolongatus Carpenter, 1863; Pliocene–Recent of North Pacific) (Moore 1992: pl. 5, figs 12–14, 16) by having a subcentrally placed straight umbo, and ribs separated by wider intercostal spaces.
Kolmeris can be distinguished from Cyclocardia Conrad, 1867 (type species Cardita borealis Conrad, 1831; Pleistocene–Recent, Northwest Atlantic Ocean) (Huber 2010: p. 253) by having a smaller and subtriangular shell, with larger right anterior tooth, vertical left anterior tooth, and shell surface sculptured by fewer radial ribs.
Kolmeris differs from Scalaricardita Sacco, 1899 (type species Cardita scalaris Sowerby, 1825; lower Miocene–upper Pliocene of Europe) (Janssen & Moerdijk 2004: fig. 4) by having a more convex dorsal margin, fewer and smooth radial ribs with wider intercostal spaces.
We include three New Zealand species in Kolmeris: Pleuromeris murdochi (Powell 1938: pl. 39, fig. 6) (upper Pliocene, Castle Point Formation), Pleuromeris paucicostata (Laws 1940: figs 7–8) (upper Pliocene–Recent, Nukumaru Beds) and Venericardia (Pleuromeris) marshalli (Marwick 1924: pl. 16, figs 1–2) (upper Pliocene– Recent, Petane Clays). These species share with K. tehuelchana the same outline, the straight right anterior tooth, the right middle tooth slightly inclined posteriorly, and 9 to 15 wide radial ribs separated by wide intercostal spaces. As the New Zealand species are not older than Nukumaruan (upper Pliocene, 2–1.2 Ma sensu Haywick et al. 1991); K. tehuelchana (lower Pliocene) becomes the oldest member of the genus.