Miquel and Rodriguez—Terrestrial gastropods from Santa Cruz
living in South America were described from Juan Fernández Archipelago, P. conicum Odhner 1922, and P. depressum Odhner 1922, whose identities are confirmed here through examination of new material. Although the only specimen of P. patagonicum n. sp. is fragmentary, its shell is different from P. conicum in size: 1.95× 1.15 and 4 whorls; P. depressum is different by the faster growth of the whorls and also by its size: 1.05× 0.7mm and 3.75 whorls. Similar shells occur in charopid genera such as Radiodiscus Pilsbry and Ferriss 1906, and Retidiscus Fonseca and Thomé 1995, where a reticulated sculpture is based on axial costulae and marked spiral incisurae (Miquel and Cádiz Lorca, 2008).
Other recent materials compared.—Punctum conicum Odhner 1922: MACN-In 39491. Col. M. Ramírez, E. Soto and J. Pizarro, 20-II-2011. Two specimens. P. depressum Odhner 1922: MACN-In 39492. Col. M. Ramírez, E. Soto and J. Pizarro, 20-II-2011. Two specimens.
Family Charopidae Hutton, 1884 Genus Zilchogyra Weyrauch, 1965
Type species.—Helix costellata Orbigny 1835, by original designation.
Occurrence.—The current range of this genus covers tropical areas of South America, including at least Peru, Brazil, Chile and Argentina (Fernández, 1973; Flórez Bustamante, 1968; Hylton Scott, 1970; Miquel et al. 2007; Miquel and Barker, 2009; Weyrauch, 1965). Middle Eocene–Recent (Miquel and Bellosi, 2010).
Zilchogyra miocenica new species Figure 6.1–6.3
Diagnosis.—Shell of low helicoid shape, with 4.5 very convex whorls; protoconch with 1.75 smooth whorls; teleoconch with marked irregularly axial ribs (approximately 90 on last whorl) and weak axial costulae.
Etymology.—Feminine. Belonging to the Miocene.
Examined material.—MPM PI 3319: Holotype. MPM PI 3320: One Paratype (illustr.). MPM PI 3321-3335: Fifteen Paratypes.
Geographical provenance.—‘Puesto de la Estancia La Costa’ (=Corriguen Aike; 51° 12’ 8.2” S and 69° 03’ 35.6” W), between the Coyle and Gallegos inlets.
Stratigraphical provenance.—Santa Cruz Formation, late Bur- digalian/early Langhian, Early-Middle Miocene (between 18 and 15 Myr.). Fossiliferous Level 6 of Tauber (1997a), late Burdigalian, ~17.5 Myr. (Fleagle et al. 2012).
Description.—Shell discoidal of medium height, low helicoid, with 4.5 regular and convex whorls, suture deep; protoconch with 1.75 smooth whorls; teleoconch with very prominent, irregular axial ribs, approximately 50 on the first adult whorl,
Figure 6. Zilchogyra miocenica n. sp.: (1) MPM PI 3319, holotype, apical view; (2) MPM PI 3320, paratype, detail of umbilicus and protoconch; (3) MPM PI 3321, paratype, umbilical view. Scale bars represent 500 µm (1, 3) and 100 µm(2).
90 on last whorl, and delicate axial ribblets; umbilicus perspective (35% of major diameter), and aperture enlarged.
Measurements.—Holotype: 2.5 ×1.95mm, 4.5 whorls; Paratype: 2.6× 2.5mm, 4.5 whorls.
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