Kolmeris tehuelchana ( Ihering, 1907 )

Pérez, Damián E. & Del Río, Claudia J., 2017, Systematics of the family Carditidae (Bivalvia: Archiheterodonta) in the Cenozoic of Argentina, Zootaxa 4338 (1), pp. 51-84 : 68-69

Kolmeris tehuelchana ( Ihering, 1907)

Figure 5.3–6

v*1907 Venericardia tehuelchana Ihering , p. 412–413, pl. 16, figs 107a–b. v.1907 Venericardia dalli Ihering , p. 413, pl. 16, figs 108a–d.

1914 Venericardia tehuelchana Ihering—Ihering , p. 45.

v.1933 Venericardia dalli Ihering—Feruglio , p. 96, pl. 8, figs 4–7. v1933 Venericardia tehuelchana Ihering—Feruglio , p. 96, pl. 8, figs 1–3. 1996 Venericardia tehuelchana Ihering—Parodiz , p. 273.

Type specimens. Holotype MACN-Pi 371, one left valve from Terraces of Cerro Laciar ( Feruglio, 1954) (Santa Cruz Province) . Paratypes MACN-Pi 371, nine left and eight right valves from Terraces of Cerro Laciar ( Feruglio, 1954) (Santa Cruz Province) .

Other material. MACN-Pi 353 (Holotype of Venericardia dalli ), 2214, 6334; PRI.66711 (83 left valves and 100 right valves).

Diagnosis. Shells with long dorsal margin with a pronounced slope. Left anterior tooth elongate. Radial ribs (13 to 15) with subrectangular transverse section, increasing in width towards ventral margin, stacking towards posterior and anterior margins. Intercostal spaces with subrectangular transverse section.

Description. Shell small-sized (maximum size of 16 mm), subtriangular, higher than long; posterior margin rounded forming a slight angle with ventral one, dorsal margin convex and long nearly vertical, descending in a strong slope, ventral and anterior margins rounded. Umbo pointed, placed at centre of valve length. Lunule large, flat, elongate, demarcated by a deeply incised groove.

Right valve hinge with concave ventral edge; anterior tooth very small, thin, short, straight, inclined anteriorly, with concave anterior side; middle tooth triangular, slightly inclined posteriorly, with straigth anterior side and higher towards apex on lateral view; posterior tooth very thin and slightly curved. Left valve hinge with a concave ventral edge; elongate anterior tooth, triangular, straight, with straight anterior and posterior sides; posterior tooth elongate and straight.

External sculpture of 13 to 15 entire and low radial ribs of triangular transverse section, widening towards ventral margin; shallow intercostal spaces of subrectangular transverse section, narrower than radial ribs; ribs stacking and narrowing towards anterior and posterior sides with 3 to 6 radial ribs, leaving 3 to 6 wide radial ribs at central region. Pallial line one-fourth of total valve height. Inner ventral margin strongly crenulated, crenulations subrectangular, truncated covering entire margin.

Remarks. Ihering (1907) described Venericardia dalli from the same locality as K. tehuelchana , with the only major difference being the number of stacked radial ribs on the valve flanks, four in V. dalli and six in K. tehuelchana . By observing many specimens of K. tehuelchana , we found the number of stacked ribs ranged from three to six. Venericardia dalli is considered synonymous with K. tehuelchana , therefore.

Kolmeris tehuelchana can be distinguished from K. murdochi ( Powell, 1938) (upper Pliocene, New Zealand) by having a more pronounced sloping dorsal margin, a longer left anterior tooth and fewer radial ribs that are stacked on the flanks.

Kolmeris tehuelchana and K. paucicostata ( Laws, 1940) (Pliocene–Recent, New Zealand) has a shell of similar outline and size, but the Patagonian species has a longer left anterior tooth and more radial ribs that are stacked on its flanks.

Kolmeris tehuelchana differs from K. marshalli ( Marwick, 1924) (upper Pliocene–Recent, New Zealand) by having a higher number of radial ribs that are stacked on the flanks and ribs that are wider towards the ventral margin.