Bienvillia sp.

Taylor, John F., Loch, James D. & Repetski, John E., 2024, Taxonomy and stratigraphic distribution of Lotagnostus (Agnostida: Agnostidae) and associated trilobites and conodonts in the Upper Cambrian (Furongian) of Laurentia, Zootaxa 5422 (1), pp. 1-66 : 28-29

Bienvillia sp.

( Plate 4 )

Material and occurrence. Lotagnostus rushtoni Fauna : 5/22/08C (11-0-1), 5/22/08D (15-0-0), and D3383-CO (3- 0-0) from Ninemile Canyon, Nevada.

Discussion. The species of Bienvillia in the Lotagnostus rushtoni Fauna differs from B. eurekensis in displaying a shorter preglabellar field and S1 furrows that are connected across the axis. Bienvillia sp. is most similar to

B. corax , displaying most of the characteristic features of the holotype cranidium, which was well illustrated by Ludvigsen et al. (1989, pl. 4, fig. 18). The shape and position of the four pairs of glabellar furrows are similar, although the S4 furrows are even more weakly developed than those of the holotype, and are not discernible at all on most specimens. Like the holotype, the better preserved cranidia of Bienvillia sp. have a bluntly pointed anterior margin, and a preglabellar field that is longest (sag.) at the midline and tapers slightly abaxially. However, Bienvillia sp. displays a shorter (sag.) and more convex preglabellar field and a more quadrate glabella that is nearly parallel-sided and less evenly rounded anteriorly. The other cranidia identified as B. corax by Ludvigsen et al. (1989, pl. 4, figs 19–22) show significant variation in these features, much of it clearly ontogenetic, and collectively provide a broad species concept in which the Windfall species could be accommodated. However, the trend in ontogenetic variation suggested by their material is opposite to that displayed by the specimens of Bienvillia sp. in the Windfall. In Bienvillia sp. , the smaller cranidia display more quadrate, parallel-sided and anteriorly truncate glabellae, as compared to somewhat more circular and anteriorly rounded glabellae in larger sclerites from the same collection. In contrast, the glabellae of the smallest cranidia of B. corax figured by Ludvigsen et al. (1989) are more circular than the larger cranidia, a trend well illustrated by the two cranidia they illustrate from the same collection ( Ludvigsen et al., 1989, pl. 2, figs 19, 22). Given these differences, and the relatively small number and poor quality of the compacted and deformed cranidia from the Windfall, we consider it best to leave the species in the Lotagnostus rushtoni Fauna in open nomenclature.

An older species designated Bienvillia cf. B. corax by Ludvigsen et al. (1989) in their Onchontus richardsoni Fauna resembles our younger species in the Windfall in the shape and proportions of the glabella. However, B. cf. B. corax differs from both the Windfall species and B. corax in the transverse (as opposed to oblique) orientation of the F3 furrows, and better development of a palpebral ridge. Additionally, B. cf. B. corax displays neither the pointed anterior margin nor the lengthening (sag.) of the preglabellar field sagitally seen in those younger species. The position of the intersection of the occipital furrow and the axial furrow also differs. In Bienvillia corax and Bienvillia sp. , that junction lies well in front of the proximal end of the posterior border furrow. On B. cf. B. corax cranidia, the occipital furrow does not curve forward as strongly as it approaches the axial furrow, so the intersection lies barely in front of the posterior border furrow.

Figures

PLATE 4. Bienvillia sp. All cranidia except 7 (librigena). Each white scale bar represents 2mm. 1-2. USMN 775718, from D3383-CO, dorsal and anterior views. 3-4. CM 41327, from 5/22/08C, dorsal and right lateral views. 5-6. CM 41328, from 5/22/08D, dorsal and left lateral views. 7. Right librigena, CM 41329, from 5/22/08C, dorsal view. 8. CM 41330, from 5/22/08C, dorsal view. 9. CM 41331, from 5/22/08C, dorsal view. 10. CM 41332, from 5/22/08D, dorsal view. 11. CM 41333, from 5/22/08D, dorsal view. 12. CM 41334, from 5/22/08D, dorsal view. 13. CM 41335, from 5/22/08D, dorsal view. 14. CM 41336, from 5/22/08D, dorsal view. 15. CM 41337, from 5/22/08C, dorsal view.