Blountia janei Lochman, in Lochman & Duncan, 1944

Westrop, Madison Armstrong Stephen R. & Eoff, Jennifer D., 2020, Systematics of a survivor: the Cambrian kingstoniid trilobite Blountia Walcott, 1916 across the Marjuman-Steptoean (Guzhangian-Paibian) extinction interval in Laurentian North America, Zootaxa 4804 (1), pp. 1-79 : 13

Blountia janei Lochman, in Lochman & Duncan, 1944

Plate 7, figs 1–10, Plate 8

1944 Blountia janei Lochman, in Lochman & Duncan , p. 52, pl. 8, figs 1–6.

non 2000 Blountia janei Lochman, in Lochman & Duncan ; Stitt & Perfetta, p. 213, fig. 11.14–11.17 [= Blountia sp. indet].

Diagnosis. Anterior cranidial margin broadly rounded. Frontal area equal to about one-third (31%; 27–34) of cranidial length. Anterior border furrow shallow; preglabellar field and anterior border subequal in length. Anteriorly rounded, subtrapezoidal glabella with strong convexity. Elongate, semielliptical pygidium, length nearly threequarters of maximum width (72%; 69–75), with faint border furrow; axial furrows become effaced posteriorly in larger specimens. Axis short, occupying 75% (74–78) of pygidial length; six axial rings, with three short segments incorporated into terminal piece (Pl. 7, figs 4–7).

Material. Holotype cranidium ( USNM 127144 , Pl. 8, figs 3–5), two paratype cranidia ( USNM 122149, Pl. 8, figs 1, 2; USNM 127150 , Pl. 8, figs 6, 7), and four pygidia ( USNM 127145 a, Pl. 7 figs 1–3; USNM 127145 b, Pl. 7, figs 4–6; USNM 127146 , Pl. 10, fig. 7; USNM 127149 , Pl. 8, fig. 8) from the Pilgrim Formation, Half Moon Pass section ( Lochman & Duncan 1944), Big Snowy Mountains , Montana.

Occurrence. Crepicephalus Zone, Pilgrim Formation, Half Moon Pass section, Lochman & Duncan’s (1944) horizons 9.1, 9.1a, 9.1x, and 9.2, Big Snowy Mountains , Montana.

Discussion. The distinctive, elongate pygidium with a short axis and weak border furrow (Pl. 7, figs 1–8) separates B. janei from other species assigned to Blountia . The cranidium is most like B. angelae (Pl. 15, figs 1–5), in possessing an evenly rounded anterior cranidial margin and a subtrapezoidal, anteriorly rounded glabella, although B. janei has slightly bowed sides, and posterolateral projections that curve posteriorly. The pygidium of B. angelae (Pl. 15, fig. 7–9) differs clearly in having longer axis with seven, rather than six segments in front of the terminal piece, and has a firmly impressed border furrow even on testate surfaces (Pl. 15, fig. 6).

Sclerites from the Deadwood Formation that were assigned to B. janei by Stitt and Perfetta (2000) do not belong to that species, and their status is uncertain. The pygidia ( Stitt & Perfetta 2000, fig. 11.16, 11.17) are shorter and wider than any in Lochman & Duncan’s type lot (Pl. 7, figs 1–8). The cranidia ( Stitt & Perfetta 2000, fig. 11.14, 11.15) have noticeably shorter anterior borders than the holotype (Pl. 8, figs 3–5) and paratype (Pl. 8, figs 1, 2, 6, 7) cranidia from Montana.