Lotagnostus, Whitehouse, 1936

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 : 47

Lotagnostus aff. L. clarki

( Plate 6.4–6.10)

1860 Agnostus americanus Billings ; Billings, p. 303, fig. 1b.

1865 Agnostus americanus Billings, 1860 ; Billings, p. 395, fig. 372b.

1944 Agnostus americanus Billings, 1860 ; Rasetti, p. 233, pl. 36, fig. 1.

1989 Lotagnostus americanus ( Billings, 1860) ; Ludvigsen & Westrop in Ludvigsen, Westrop, and Kindle, p. 12, pl. 1, fig. 16. 2005 Lotagnostus americanus ( Billings, 1860) ; Peng & Babcock, p. 110–113, fig. 2.3.

2009 Lotagnostus americanus americanus ( Billings, 1860) ; Rushton, p. 276, fig. 1J–O.

2011 Lotagnostus americanus ( Billings, 1860) ; Westrop, Adrain, & Landing, p. 578–584, figs 5D–G, 6.

2015 Lotagnostus americanus ( Billings, 1860) ; Peng, Babcock, Zhu, Ahlberg, Terfelt, & Dai, fig. 5G.

Discussion. The restriction of Lotagnostus americanus to the holotype necessitates re-evaluation of the remaining material from the Lévis Formation formerly assigned to that species. Although the pygidia are indistinguishable from those of L. clarki , the cephala differ in the structure of M2, M3, and the anteroglabella. M2 on L. aff. L. clarki is equal in width (tr.) to M1 and narrower than M3, whereas M2 on L. clarki is wider than both M1 and M3. The lateral lobes of M3 on L. aff. L. clarki are nearly circular in shape, whereas those of L. clarki are more elongate and taper posteriorly. In some specimens of L. aff. clarki they display greater inflation with the distal sides bowing more strongly outward. The species from the Lévis also appears to have a proportionally longer anteroglabella. The ratio between the axial length of the anteroglabella (AAL) and that of the posteroglabella (APL) obtained from L. clarki cephala varied from 0.47 to 0.54, with an average of 0.49. Unfortunately, only three of the seven cephala from the Lévis Formation illustrated by Rushton (2009) and Westrop et al. (2011) were preserved well enough for accurate measurement of the AAL/APL ratio. Nonetheless, two of those specimens yielded values (0.56, 0.62) outside the range documented for L. clarki cephala.