Jardamarekia enigma, Frýda, Jiří, Blodgett, Robert B., Lenz, Alfred C. & Frýdová, Barbora, 2011

Frýda, Jiří, Blodgett, Robert B., Lenz, Alfred C. & Frýdová, Barbora, 2011, Jardamarekia enigma, a new Early Devonian tryblidioidean from Royal Creek area (Yukon Territory, Canada), and paleobiogeography of the Early Devonian of northwestern Canada, Zootaxa 2905, pp. 57-62 : 60

Jardamarekia enigma sp. nov.

Fig. 2 A–N

Holotype. GSC 134793 ( Fig. 2 A–C, F, H–N).

Paratype. GSC 134794 ( Fig. 2 D–E, G).

Type locality. Middle Early Devonian (Pragian) age strata of the Road River Formation in the Royal Creek area, Yukon Territory, Canada. It comes from interval 142.0–150.0 m (466–492 feet) of section 1 ( Fig. 1 ), which belongs to the fauna of Pragian age with the brachiopod Davidsoniatrypa johnsoni Lenz, 1968 ( Lenz 1977b).

Etymology. enigma —from Latin aenigma (something inexplicable).

Diagnosis. Because of monotypic genus, see that of genus.

Description. Two well-preserved, silicified, almost complete shells. Shells medium-sized, spoon shaped with distinctly protruding apex; maximum length about 27 mm. Shell as high as wide, twice as long. Aperture elliptical, apertural margin in one plane. Protruding shell apex in middle of shell height, distinctly overhanging anterior margin of aperture ( Fig. 2 C–E). Outer shell surface ornamented by strong concentric lamellae, comarginal with aperture. Lamellae crossed by radial threads. Comarginal lamellae, radial threads regularly spaced, forming distinct reticular shell ornamentation at their intersections ( Fig. 2 A–C, J, K). Distance between lamellae about twice distance between radial threads. Because of more rapid shell growth in dorsal part of shell, distance between comarginal lamellae in dorsal region higher than in anterior region below shell apex. Lamellae adapically bent, height equals to their distance of separation. Width of each lamella about half of its height ( Fig. 2 M–N). Shell apex blunt, cap-shaped without traces of spiral coiling ( Fig. 2 C, H–I). Shell thickness about equal to width of comarginal lamellae ( Fig. 2 N).

Figures

FIGURE 1. A—Stratigraphic section 1 showing a distribution of all hitherto described molluscs species from Royal Creek, northern Yukon. B—Generalized maps showing location of section 1 (asterisk) in the Yukon Territory, Canada. Modified from Lenz (1977 b).

FIGURE 2. Jardamarekia enigma sp. nov. from middle Early Devonian (Pragian) age strata of the Road River Formation in the Royal Creek area, Yukon Territory, Canada. The species is from interval 142.0 – 150.0 m of section 1 (Fig. 1 A). Holotype GSC 134793: A – C, F, H – N, shell length 18 mm, width 14 mm, height 10 mm; figure width of shell details: H— 11 mm, I— 10 mm, J— 8 mm, K— 3,5 mm, L— 10 mm, M, N— 3 mm. Paratype: GSC 134794: D – E, G, shell length 26 mm, width 21 mm, height 11 mm.