Blountia cora 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 : 12-13

Blountia cora Lochman, in Lochman & Duncan, 1944

Plate 6, Plate 7, figs 11–14

1944 Blountia cora Lochman, in Lochman & Duncan , p. 51, pl. 8, figs 7–11.

non 2000 Blountia cora Lochman, in Lochman & Duncan ; Stitt & Perfetta, p. 213, figs 11.6–11.7 [= Blountia sp. indet.].

Diagnosis. Anterior cranidial margin evenly rounded; very long frontal area occupies slightly more than one-third (37%; 35–39) of total cranidial length (shorter in small cranidia; Pl. 7, figs 11–13), roughly equally divided into preglabellar field and gently upturned anterior border; differentiated by shallow border furrow and change in slope. Anterior branches of facial sutures diverge forward. Wide palpebral areas of fixigenae account for about half (48%; 47–49) cranidial width; posterolateral projection deflected sharply backward. Semielliptical pygidium, with length slightly less than two-thirds (63%; 63–64) maximum width (smaller pygidia [e.g., Pl. 6, fig. 9] are relatively short- er), with shallow border furrow. Axis becomes indistinct posteriorly in larger specimens (Pl. 7, fig. 9).

Material. Holotype cranidium ( USNM 127151 , Pl. 6, figs 1–3), three paratype cranidia ( USNM 127153 , Pl. 6, figs 4–7, Pl. 7, figs 11–13) and three paratype pygidia ( USNM 127152 b, Pl. 7, figs 4–6; USNM 127153 , Pl. 6, figs 8, 9, Pl. 7, fig. 14) 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, 9.1x, and 9.2, Big Snowy Mountains , Montana.

Discussion. A cranidium and pygidium from the lower Deadwood Formation of the Black Hills, North Dakota, were illustrated as Blountia cora by Stitt and Perfetta (2000, fig. 11.6, 11.7), but are almost certainly misidentified. The cranidium is too poorly preserved and illustrated for a comprehensive evaluation but appears to have an anterior border that is noticeably shorter than the preglabellar field, whereas they are subequal in length in the types of B. cora (Pl. 6, figs 1–7). In addition, the anterior branches of the facial sutures of this specimen appear to be subparallel, rather than conspicuously divergent, as in the types. The pygidium from the Deadwood Formation is narrower than any of the types (Pl. 6, figs 8, 9; Pl. 7, figs 8, 9, 14) but, because it is illustrated in dorsal view only, additional comparisons are difficult.

Cranidia of B. cora and B. angelae share an evenly rounded anterior margin, long frontal area, subtrapezoidal, anteriorly-rounded glabella, wide palpebral areas of the fixigenae, and posterolateral projections are deflected pos- teriorly with expansion of the posterior border (e.g., compare Pl. 8, figs 1–3 and Pl. 15, figs 1–3). They differ in frontal area proportions, with a shorter preglabellar field in the latter that occupies 37% of frontal area length, versus 43% in B. cora . Pygidia are clearly differentiated in the expression of the border and pygidial axis, both of which are well defined in B. angelae (e.g. Pl. 15, fig. 6). In contrast, the border furrow of B. cora is weak to entirely effaced, and the axis becomes indistinct posteriorly during holaspid ontogeny (Pl. 6, figs 8, 9, Pl. 7, figs 9, 10, 14). Moreover, the largest available pygidia of B. cora (Pl. 7, fig. 9, 10) is about half the size of the well-furrowed pygidium (Pl. 15, fig. 6) of B. angelae , indicating that effacement occurs early in the ontogeny of the former.

Cranidia of B. alexas Walcott, 1916 ( Rasetti 1965, pl. 9, figs 9–12), from the Nolichucky Formation of northeastern Tennessee, have backwardly swept posterolateral projections that resemble the condition in B. cora , but the frontal area is much shorter, and the palpebral area of the fixigena is narrower.