Serenida dorsoplicata, 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 : 819-821

Serenida dorsoplicata sp. nov.

Fig. 3K, L, M.

Holotype: IRScNB n ° b4504. Carapace. DVG−03−19. Fig. 3K 1 , K 2. L = 0.73 mm; H = 0.48 mm; W = 0.30 mm.

Type horizon: Lower member of the Devils Gate Limestone. Near top of Palmatolepis punctata Zone.

Type locality: Devils Gate, close to Eureka in Nevada.

Derivation of the name: From the Latin dorsum —back and plicatus — folded. Referring to the slant dorsal fold.

Diagnosis.— Serenida dorsoplicata sp. nov. differs from other species of the genus in having a well−developed dorsum and a short dorsal fold directed forward, and forming an angle between 10 and 20 ° with the dorsal border.

Material.—12 carapaces, 12 valves and 15 fragments.

Description.—Medium−sized sub−elliptic Serenida with a nearly straight dorsal border except just posterior to the mid−length where it is slightly curved for a short distance. Ventral border regularly curved but slightly more posteriorly. Anterior border regularly rounded, and posterior border more curved dorsally than ventrally. Greatest length a little above mid−height, and greatest height at 4/7 th of the length. Right valve larger than left valve and overreaching the left, especially ventrally, all along the margin. Ventral contour of left valve nearly straight, and posterior curvature of this valve more accentuated than on the right valve. Anterior and dorsal borders of left valve similar to the right one. Valves slightly depressed in the mid−dorsal sector. Short dorsal fold beginning along the dorsal border at 4/7 th of the length, directed forward, and forming an angle between 10 and 20 ° with the dorsal border. In dorsal view, the hinge line is straight and depressed within a well−developed dorsum. The mid−length dorsal depressions are slightly visible in dorsal view on the two valves, which are flattened at mid−length and angular anteriorly and posteriorly. Greatest width at 3/5 th of the greatest length. Surface of valves smooth.

Remarks.— Serenida dorsoplicata . sp. nov. is similar in lateral outline to Serenida tenuisulcata Rozhdestvenskaja, 1972 , and Serenida costulata Rozhdestvenskaja, 1972 , from the Upper Devonian of Baschkiria, however, the dorsal overreach is not as great in these two species, and they do not possess a dorsal fold. The carapace of S. tenuisulcata is also thicker. The Kloedenellid sp. 44 from the Great Slave Lake region ( Canada), figured by Braun (1967: pl. 6), belongs probably to S. dorsoplicata sp. nov.

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.