Beyrichona tinea Matthew, 1886

Álvarez, María Eugenia Dies, Gozalo, Rodolfo, Cederström, Peter & Ahlberg, Per, 2008, Bradoriid arthropods from the lower-middle Cambrian of Scania, Sweden, Acta Palaeontologica Polonica 53 (4), pp. 647-656 : 650

Beyrichona tinea Matthew, 1886

Fig. 3A, B.

1886 Beyrichona tinea sp. nov.; Matthew 1886: 66, pl. 6: 21, 21a, b.

1997 Beyrichona tinea Matthew, 1886 ; Siveter and Williams 1997: 42–43, pl. 5: 2–12 [see for complete synonymy].

2007 Beyrichona tinea Matthew ; Williams et al. 2007: fig. 5.2.

Material.—Three nearly complete left valves of which LO 9347t ( Fig. 3A 1, A 2) is largely exfoliated and LO 9348t ( Fig. 3B 1, B 2) is original carapace.

Diagnosis (after Siveter and Williams 1997).—Species of Beyrichona with prominent anterior lobe and sub−circular anterodorsal sulcus. Ventral part of lateral outline gently convex. Valve length subequal to or less than valve height.

Description.—Slightly postplete valves with sub−triangular outline. Dorsal margin straight, 70–75% of valve length. Lateral outline curved anterodorsally and ventrally, and gently convex posteriorly. Trilobate; lobes developed dorsally, confluent ventrally with broadly convex lateral surface. Prominent and sub−conical anterior lobe overreaching dorsal margin. Sub−circular anterodorsal sulcus. Central lobe broad, gently convex. Subdued, gently convex posterior lobe. Posterior sulcus narrow, weakly developed. Marginal ridge entire between cardinal corners, broadest anterodorsally. Valve surface smooth.

Remarks.—The valves agree in all essential respects with those of B. tinea from New Brunswick. The main difference is the sub−conical morphology in the anterodorsal lobe in specimens preserved with the original carapace (e.g., Fig. 3B 1, B 2). In the largely exfoliated specimen ( Fig. 3A 1, A 2), the morphology of this lobe is very similar to the Canadian specimens. Another minor difference is that the central lobe is narrower in the Scanian material and the posterior sulcus is slightly broader than in the Canadian material. These differences are here considered to be of minor taxonomical importance and our material is assigned to B. tinea .

Stratigraphic and geographic distribution.—Upper part of the traditional lower Cambrian in New Brunswick, eastern Canada (Hanford Brook Formation, Protolenus elegans Zone ; Siveter and Williams 1997), and Scania, southern Sweden (upper Gislöv Formation, Ornamentaspis ? linnarssoni Zone). Possibly also from the?lower Cambrian of the Gulf of Bothnia ( Siveter and Williams 1997).