Voronina? eureka, Casier & Berra & Olempska & Sandberg & Préat, 2006

Casier, Jean-Georges, Berra, Ivan, Olempska, Ewa, Sandberg, Charles & Préat, Alain, 2006, Ostracods and facies of the Early and Middle Frasnian at Devils Gate in Nevada: Relationship to the Alamo Event, Acta Palaeontologica Polonica 51 (4), pp. 813-828 : 821

Voronina? eureka sp. nov.

Fig. 3N, O, P.

Holotype: IRScNB n ° b4507. Carapace. DVG−03−4. Fig. 3N 1 , N 2. L = 1.10 mm; H = 0.75 mm; W = 0.44 mm.

Type horizon: Lower member of the Devils Gate Limestone.Late Mesotaxis falsiovalis Zone.

Type locality: Devils Gate, close to Eureka, Nevad.

Derivation of the name: Referring to the town Eureka, Nevada, close to the Devils Gate section.

Diagnosis.— Voronina? eureka sp. nov. differs from other species of the genus in having highly asymmetric valves and a thickening along the dorsal border of right valve.

Material.—71 carapaces, 6 valves, and about 175 fragments.

Description.—In left−lateral view, a medium−sized sub−elliptic Voronina . Curvature of the dorsal border maximum at mid−length, and of the ventral border, slightly behind the mid−length, however, both are regularly curved in young in−

stars. Anterior border more curved ventrally, and anterior extremity slightly below mid−height. Posterior border regularly curved with extremity at mid−height. Greatest length at mid−height, and greatest height just behind mid−length. Right valve larger than left valve and overreaching the left all along the margin, especially dorsally and ventrally. Dorsal border of left valve nearly straight, ventral border occasionally very slightly concave, and anterior and posterior borders approximately parallel to the right valve. Right valve thickened along the dorsal border, fusiform in dorsal view with the extremity occasionally slightly pinched. Dorsal thickening of left valve very prominent. Greatest width at mid−length or slightly behind mid−length. Surface of valves smooth.

Remarks.—In lateral view Voronina? eureka sp. nov. is similar to Voronina voronensis Polenova, 1952 , the type species for the genus. However, the dorsal view is quite different because the left valve of V. voronensis possesses a posterior thickening. V. voronensis is known from the Middle Devonian (Givetian) of Pachelma in Penza area, and also of the Tambov and Kaluga areas, all on the Russian Platform. Voronina cornuta Egorova, 1960a , V. longula Egorova, 1960a , V. sulcata Egorova, 1960a and V.? remosa Averjanov and Egorova, 1960 in Egorova (1960b) are Eifelian in age. Voronina? eureka sp. nov. is present only in two samples DVG−03−4 and DVD−03−6.

Uncertain family

Genus Westmontia Loranger, 1963

Westmontia devilensis Casier and Lethiers, 1997 ( Figs. 3Q, 4A, B).—This highly polymorphic species, previously identified in the Late Frasnian and Early Famennian of the Devils Gate section ( Casier and Lethiers 1996, 1997), displays five variably developed lobes, and a slightly to heavily reticulated ornamentation. Westmontia devilensis is a relatively abundant species from DVG21b upward. Westmontia sp. 257 sensu Braun (1967), from the Great Slave Lake region ( Canada), and maybe also an instar described by Lethiers (1981) from the Root River, in the Northwestern Territories ( Canada), belong to W. devilensis .

Platycopina indet. ( Fig. 4C).—A finely ornamented but poorly preserved carapace from sample DVG−03−A12 is assigned to the Platycopina .

Figures

Fig. 1. Location of the Devils Gate section, Nevada (after Casier et al. 1996).

Fig. 2. Lithology of the lower member of the type Devils Gate Limestone showing positions of ostracod, conodont, and sedimentological samples. Ostracod samples numbered DVG are from Sandberg et al. (1988, 2003). Other columns indicate conodont zones revised herein by Sandberg, paleoenvironmental interpretation, and microfacies evolution. Abbreviation: Pa., Palmatolepis.