Raphistomatidae Koken, 1896

Family Raphistomatidae Koken, 1896 View in CoL

[= Ceratopeidae Yochelson & Bridge, 1957 ]

Genus Scalites Emmons, 1842

Type species: Scalites angulatus Emmons 1842 , by monotypy; from the Chazy Group of the Middle Ordovician, North America .

Remarks.—Based on phylogenetic analyses, Wagner (2002) suggested including within Scalites all species previously classified as Raphistoma Hall, 1847 . According to that author, the type species S. angulatus shares several synapomorphies with Raphistoma , and thus, he pointed out that it would be more consistent with the phylogeny to use Scalites for the species of Raphistoma . Members assigned to Scalites are diagnosed by flattened ramps that (owing to the overall orientation of the aperture) are nearly perpendicular to the coiling axis, strong adapically hooked peripheral bands, and strong channeled basal carina ( Wagner 2002).

Stratigraphic and geographic range.—Lower Ordovician– Silurian of North America, Europe and South America.

Scalites peracutum ( Ulrich & Scofield, 1897)

Fig. 3D–G View Fig .

1897 Raphistoma peracuta Ulrich & Scofield, 1897 .

1928 Raphistoma peracuta Ulrich & Scofield, 1897 ; Twenhofel 1928: 236.

1987 Rhaphistoma peracuta Ulrich & Scofield, 1897 ; Sloan and Webers 1987: 185.

2002 Scalites peracutum ( Ulrich & Scofield, 1897) ; Wagner 2002: 74.

2020 Scalites peracutum ( Ulrich & Scofield, 1897) ; Bertero 2020: 59, pl. 4: 3–7.

Material.— CEGH-UNC 24783–24794, CEGH-UNC 24771– 24773; twelve recrystallized teleoconchs and three moulds from Sierra Villicum and Quebrada Don Braulio localities, Argentina, Sandbian , Upper Ordovician.

Description.—Lenticular, phaneromphalous, medium to small sized and low-spired shell with the upper surface nearly flat to convex. The height is 70 mm and the width is 20– 35 mm. The teleoconch has a subtriangular shape in transversal view and consists of four whorls ( Fig. 3D View Fig ). Sutures are deeply incised in a spiral furrow. The peripheral selenizone is slightly wide and flat and bears prosocline lunulae. The ornament on the upper whorl consists of fine and strongly prosocline growth lines ( Fig. 3E View Fig , fragmentary ornament pattern on the periphery of last whorl). The base is flat and angular ornamented by prosocline growth lines. The umbilicus is wide, deep and funnel shaped, ornamented by acute axial ribs with a prosocline and orthocline orientation at regular intervals followed by a slightly flared increment ( Fig. 3G View Fig ). The axial ribs are intercepted by two acute spiral ribs. A sharp basal carina with rounded nodes borders the umbilical area ( Fig. 3G View Fig ).

Remarks.—Representatives of Scalites shares several characters of Raphistoma Ulrich & Scofield, 1897 . Raphistoma is diagnosed by having a flat to convex shell with a triangular shape in transversal view, a flat spire, and a sharp periphery bearing the selenizone. Rohr et al. (1992) also pointed out that Scalites and Raphistoma are very similar raphistomatids, with Scalites known from three species and Raphistoma with over twenty species assigned.

The species herein described differs from the type species Scalites angulatus Emmons, 1842 ( Rohr et al. 2004), from the Middle Ordovician of North America, in having a more flattened spire, a subtriangular shell in transversal view, in lacking a thickening of the columella and strong growth lines on base, and in having a widely open umbilicus; S. angulatus is anomphalous. The specimens here described as Scalites peracutum strongly resembles the specimens of S. peracutum ( Ulrich & Scofield, 1897) from the Ordovician of North America, in general shell morphology, although the North American form is much larger. Scalites? alaskensis ( Rohr et al. 1992: 505: 3.1–7, 5), from the Middle Ordovician of Alaska, North America, has a narrowly open umbilicus, a more gradate shell, and ornament with fine spiral threads. Scalites amanoi Kobayashi, 1958 , S. keizanensis ( Kobayashi, 1934) , S. katoi Kobayashi, 1934 , and S. irregular Kobayashi, 1934 , from the Lower/Middle Ordovician of South Korea, are based on poorly preserved specimens.

Stratigraphic and geographic range.—Sandbian, Upper Ordovician, La Pola Formation, Sierra de Villicum and Quebrada de Don Braulio, San Juan Province, Argentina.