Blountia gaspensis Rasetti, 1946

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 : 14-15

Blountia gaspensis Rasetti, 1946

Plate 10, Plate 11, figs 1–4

1946 Blountia gaspensis Rasetti , p. 446, pl. 67, figs 7–10.

Diagnosis. Gently rounded anterior cranidial margin. Frontal area occupies 28% of cranidial length; down-sloping preglabellar field and slightly shorter, nearly flat anterior border differentiated largely by change in slope. Anterior border furrow shallow but clearly defined. Facial sutures diverge conspicuously anteriorly from palpebral lobes. Subtrapezoidal glabella with well-rounded front. Pygidium with short border of even width equal to about one-fifth (19%; 17–21) pygidial length (sag); separated from pleural field by strongly incised border furrow. Internal mould expresses at least nine axial rings and terminal piece of two segments, and faint, straight interpleural furrows.

Material. Holotype cranidium ( GSC 140491 [ LU 1004 a], Pl. 11, figs 1–3), a paratype cranidium ( GSC 140488 [ LU 1004 d], Pl. 10, figs 1–3), and three pygidia ( GSC 140489 [ LU 1004 b], GSC 140490 [ LU 1004 c], GSC 140492 [ LU 1004 e], Pl. 10, figs 4–9, Pl. 11, fig. 4) from lower Grosses-Roches Formation, Grosses-Roches , Matane County, western Gaspé , Quebec.

Occurrence. Lower Grosses-Roches Formation, Grosses-Roches, Matane County, western Gaspé , Quebec, boulder G28 ( Rasetti 1946) .

Discussion. Pratt (1992) suggested that Blountia gaspensis is a junior synonym of B. beltensis Duncan, in Lochman & Duncan, 1944 , but there are clear differences between these species. Paratype pygidia ( Lochman & Duncan, 1944, pl. 11, figs 20–22, 24) show that the border furrow of B. beltensis is effaced posteriorly even on internal moulds, and there is little change in slope in the lateral profile between the pleural field and border. In contrast, B. gaspensis has a conspicuous, continuous pygidial border furrow marked in part by a sharp break in slope between the pleural field and the flatter posterior border (Pl. 10, figs 4–9). Cranidia of B. beltensis appear to have a distinctly shorter preglabellar field that is roughly equal to ( Lochman & Duncan, 1944, pl. 11, fig. 25), or less than ( Lochman & Duncan, 1944, pl. 11, fig. 26 [holotype]), anterior border length. Cranidia from the Rabbittkettle Formation identified as B. beltensis by Pratt (1992, pl. 24, figs 7–9, 12) also have shorter preglabellar fields, and the pygidia resemble the types in showing effacement of the border furrow posteriorly (e.g., Pratt, 1992, pl. 24, fig. 10).

Like B. morgancreekensis (Pl. 17, figs 1–11, Pl. 18) from the Riley Formation of central Texas, B. gaspensis has a long frontal area (equal to 28% of cranidial length in both species), a glabella whose width is equal to 75% length, and divergent anterior branches of the facial sutures. However, the former differs by having a more rounded anterior cranidial margin, a shorter palpebral lobe (11% of cranidial length (sag.), versus 17% in B. gaspensis ), and a shallower anterior border furrow. The pygidia are similar in outline, and both species display a well-segmented axis on internal moulds. However, the pygidia of B. gaspensis have a more clearly defined border furrow. In addition, the sharp break in slope between the pleural field and the nearly flat border that contrasts with the more evenly downsloping border in B. morgancreekensis (compare Pl. 10, figs 6, 8 and Pl. 19, figs 3, 4, 9, 10).

Cranidia of Blountia angelae have similar proportions to B. gaspensis , although the anterior border is relatively longer, and the anterior cranidial margin is strongly rounded (compare Pl. 10, figs 1–3, Pl. 11, figs 1–3 with Pl. 15, figs 1–5). Like B. morgancreekensis , B. angelae has a more evenly down-sloping border (Pl. 15, figs 6–9) that is quite different from the topography of the border in B. gaspensis .