Blountia nasuta 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 : 15

Blountia nasuta Rasetti, 1946

Plate 12

1946 Blountia nasuta Rasetti , p. 446, pl. 67, figs 11–14.

Diagnosis. Anterior border increases in length medially, producing nasute outline; maximum length roughly equal to length (sag.) of preglabellar field. Abrupt slope change between down-sloping preglabellar field and nearly flat anterior border; shallow anterior border furrow. Palpebral lobes situated posteriorly, near mid-length of glabella. Triangular pygidium with border occupying 25% of length (sag.) but narrowing abaxially. Border furrow faint; moderately incised axial furrows that weaken at axis tip. Pleural field gently inflated above border. At least nine axial rings and short terminal piece expressed on internal moulds, as are pits corresponding to small projections on underside of exoskeleton.

Material. Holotype cranidium ( GSC 140496 [ LU 1005 a], Pl. 12, figs 1–3) a paratype cranidium ( GSC 140497 [ LU 1105 f], Pl. 12, figs 4–6), and three paratype pygidia ( GSC 140498 [ LU 1005 b], Pl. 14, figs 79; GSC 140499 [ LU 1005 e], Pl. 12, fig. 10; GSC 140500 [ LU 1005 c], Pl. 12, figs 11, 12) from the lower Grosses-Roches Formation, Grosses-Roches , western Gaspé , Matane County, Quebec ( Rasetti, 1946).

Occurrence. Crepicephalus Zone , lower Grosses-Roches Formation, Grosses-Roches , western Gaspé , Matane County, Quebec, boulder G-29 ( Rasetti 1946).

Discussion. Among species of Blountia , the nasute outline of the anterior border of the cranidium of B. nasuta is matched only in B. nevadensis n. sp. (Pl. 16, figs 1–3, 8). However, the latter species differs by having a shorter frontal area (equal to 30% cranidial length (sag.) versus 37% in B. nasuta ) and an even shorter preglabellar field (36% of frontal area length [sag.], versus 46% in B. nasuta ). The palpebral lobes in B. nasuta are more posteriorly positioned, so that the posterolateral projections are shorter (exsag.) and lack the conspicuous posterior deflection of the tips that characterizes B. nevadensis . The pygidia are dramatically different: B. nasuta (Pl. 12, figs 7–12) has a subtriangular outline with a posteriorly expanded border, and the axis has at least one more axial ring in front of the terminal piece. In contrast, B. nevadensis (Pl. 16, figs 6, 7, 9) is semielliptical in outline with a rounded posterior margin, and has a shorter (sag.) border (equal to 17% of pygidial length versus to 25% in B. nasuta ) that shows little change in length abaxially. The border furrow, although weak, is better defined than in B. nasuta .