Blountia newfoundlandensis, Westrop & Eoff, 2020

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 : 20-21

Blountia newfoundlandensis n. sp.

Plate 11, figs 5–10, Plates 20, 21.

Diagnosis. Frontal area slightly less than one-quarter (23%; 20–25) of cranidial length (lowest values in smallest individuals; e.g., Pl. 20, figs 9–11), divided into steeply sloping preglabellar field and longer (63% [58–71] of frontal area length), flat anterior border by well-incised border furrow. Pygidium semielliptical in outline, length 64% (56–58; lowest values in smallest specimen, Pl. 21, fig. 1) of maximum width. Pleural field raised above border. Border expands conspicuously towards axis, accounting for 20% (19–23) of pygidial length (sag.); border furrow weakens near axis. Axis with seven axial rings in front of terminal piece of two segments. External surface of exoskeleton smooth; internal mould lacks pitting.

Name. For the type area of the species in Newfoundland.

Material. Holotype cranidium ( GSC 140501, Pl. 20, figs 1–3), eight paratype cranidia ( GSC 140493 – 140495, Pl. 11, figs 5–10; GSC 140502 – 140506, Pl. 20, figs 3–11), and five paratype pygidia ( GSC 140507 – GSC 140511 , Pl. 21, figs 1–11) from the Downes Point Member , Shallow Bay Formation , Cow Head Peninsula, western Newfoundland. Twenty-seven cranidia and thirty-one pygidia were also available for study.

Occurrence. Aphelaspis Zone, Downes Point Member, Shallow Bay Formation , north shore of the Cow Head Peninsula, western Newfoundland, boulder CH 48.

Discussion. Blountia newfoundlandensis is sufficiently similar to B. angelae that a full description is unnecessary. Cranidia of the latter (Pl. 15, figs 1–5) differ from those of B. newfoundlandensis by having a longer frontal area (equal to 30% versus slightly less than 25% in B. newfoundlandensis ), a more rounded anterior cranidial margin, and wider palpebral areas of the fixigenae. The preglabellar field of B. newfoundlandensis dips down at a steeper slope than that of B. angelae , and the anterior border is flatter. The pygidium of B. angelae differs by having border that maintains a nearly even width along the lateral and posterior margins (e.g., Pl. 15, fig. 6), in contrast to the conspicuous adaxial expansion in B. newfoundlandensis (e.g., Pl. 21, figs 1, 9), and by the presence of pitting on the internal mould.

Comparisons with B. bristolensis , B. montanensis , B. tennesseensis , and B. morgancreekensis were presented earlier in the text. The type species, B. mimula (Pl. 1) has a pygidium in which the border furrow is nearly effaced and the border is barely differentiated from the pleural field. The palpebral lobes are farther forward in B. newfoundlandensis , so that the maximum length (exsag.) of the posterolateral projection is greater, and the posterior branches of the facial sutures are less strongly divergent (compare Pl. 1, fig. 5 with Pl. 21, figs 1, 5). Blountia janei is most clearly differentiated from B. newfoundlandensis by the relatively longer pygidium that has a shorter axis (e.g., Pl. 7, figs 1–8), and the cranidium has a longer frontal area that occupies one-third, rather than about one-quarter, of cranidial length (Pl. 8).