Scalaricardita laciarina ( Feruglio, 1954 )

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 : 76-77

Scalaricardita laciarina ( Feruglio, 1954)

Figure 6.14–16

v1933 Venericardia n.f. Feruglio, p. 96, figs. 8–11.

*1954 Venericardia laciarina Feruglio , p. 10–11, pl. 1, figs 5a–b, 6a–b, pl. 2, figs. 1–4a,b, 5–6.

Material studied. MACN-Pi 2213 (nine left valves and five right valves).

Diagnosis. Shell with subtriangular outline. Umbo subcentrally. Lunule faintly defined. Left anterior tooth large. External sculpture of 25 to 27 low radial ribs more conspicuous towards anterior margin.

Description. Shell small-sized (maximum size of 17 mm) with subtriangular outline, posterior margin slightly truncated forming a gentle angle as it meets the ventral one, dorsal margin straight and elongate sloping pronouncedly from beaks to posterior end, ventral and anterior margins rounded. Umbo placed near centre of the valves. Lunule small, narrow, flat, shallow and weak.

Right hinge with a concave ventral edge; anterior tooth very small, elongate, short, inclined forward, in contact with lunular margin; middle tooth triangular, small, inclined posteriorly base broad and with straight anterior and slightly posterior sides, higher towards base on lateral view; posterior tooth very thin and straight, extending to the apex of middle tooth. Left hinge with slightly curved ventral edge; anterior tooth triangular, elongate, high, inclined forward with straight anterior and posterior sides; posterior tooth elongate, wide and straight.

External sculpture of 25 to 27 entire radial ribs, low and wide, slightly wider towards ventral marginwith subelliptic transverse section covered with subrectangular and small closely-spaced and barely noticeable nodes; shallow and narrow intercostal spaces with subtriangular transverse section. Pallial line placed about a quarter of total valve height. Inner ventral margin strongly crenulated, crenulations subrectangular, truncated, covering entire margin.

Remarks. Feruglio (1933, 1954) described and illustrated specimens of this carditid recorderd in Cerro Laciar (lower Pliocene, Santa Cruz Province) but that type material was not available to the authors. However, the Feruglio collection housed at the MACN hosts 12 valves belonging in S. laciarina .

Scalaricardita laciarina is assigned to Scalaricardita because of its subtriangular shell with slightly truncated posterior margin, a triangular and wide right middle tooth, 23 to 27 low and wide radial ribs covered by subrectangular, elongate and closely-spaced nodes and narrow intercostal spaces.

Scalaricardita laciarina can be distinguished from S. scalaris ( Janssen & Moerdijk 2004: figs. 4a–b) by having a larger shell, subcentrally placed umbo, less-defined lunule, larger left anterior tooth, more pronounced anterior radial ribs and wider intercostal spaces.

Scalaricardita laciarina differs from S. compacta ( Tate 1886: pl. 2, fig. 13) by having more subtriangular shell with more prominent and subcentrally placed umbo.

Scalaricardita laciariana can be separated from S. subcompacta ( Ludbrook 1954: pl. 2, figs. 5 and 8) by a more subtriangular shell with subcentrally placed umbo and larger right anterior tooth.

This species differs from S. miniscula ( Bartrum & Powell 1928: fig. 12) by having more subtriangular shell and more radial ribs.

Scalaricardita laciarina differs from S. camaronesia by having a larger shell, less anteriorly placed umbo and narrower right middle tooth.

[ Figure 3 ]

Figures

FIGURE 3. (1 – 3) Cyclocardia cannada (Ihering, 1907). 1, LV, Holotype MACN-Pi 344, from Cañadón de los Artilleros. 2, LV, MACN-Pi 344, from Cañadón de los Artilleros. 3, RV, MACN-Pi 348, from Yegua Quemada. (4 – 6) Cyclocardia compressa (Reeve, 1843). 4, LV, MACN-Pi 363, from Puerto Deseado. 5, LV, MACN-Pi 363, from Puerto Deseado. 6, RV, MACN-Pi 363, from Puerto Deseado. (7 – 9, 11) Cyclocardia dalek n. sp. from Playa La Mina. 7, LV, Holotype MACN-Pi 5770. 8, LV, Holotype MACN-Pi 5770. 9, RV, Paratype MACN-Pi 5771. 11, RV, Paratype MACN-Pi 5771. (10, 12 – 13) ‘ Cyclocardia ’ nortensis (del Río, 1986), from Punta Norte. 10, LV, Holotype CPBA 13242. 12, RV, Paratype CPBA 13247. 13, RV, Paratype CPBA 13247. Scale bar represents 10 mm.