Blountina 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 : 23

Genus Blountina Lochman, in Lochman & Duncan, 1944

Type species. Blountina eleanora Lochman, in Lochman & Duncan, 1944 from the Pilgrim Formation, Half Moon Pass, Big Snowy Mountains , Montana (by original designation) .

Diagnosis. Strongly furrowed with long anterior cranidial border occupying 62% (60–66) of short frontal area. Tips of posterolateral projection strongly deflected backward. Pygidial border furrow nearly effaced; border flexed steeply downward.

Discussion. Opinions on Blountina Lochman have varied. Shaw (1952) considered the genus to be a junior synonym of Protillaenus Raymond 1937 , whereas Rasetti (1956) treated both Blountina and Protillaenus as synonyms of Maryvillia . Restudy of the type species, Blountina eleanora Lochman (Pls 26, 27), shows that it lacks the synapomorphies of Maryvillia (see above) and the structure of the cladogram allows Blountina to be retained for the present as a monotypic genus. A broader analysis of Kingstoniidae may help clarify its status. Cranidial characters that might diagnose Blountina include a long anterior border occupying slight more than 60% of the short frontal area, and strongly deflected tips of the posterolateral projection. The grade of effacement of the pleural field and border furrow of the pygidium (Pl. 27) resembles the condition in Kingstonia (e.g., K. gaspensis ; Fig. 1.6, 1.7), as does the strong downward flexure of the border. Although the pygidial axis is mostly effaced in K. gaspensis , other species retain a convex axis similar to that of B. eleanora (e.g., Rasetti 1946, pl. 69, fig. 31).

Blountina triangularis Lochman in Lochman & Duncan is closely related to M. arion ( Fig. 2 ), and both species are assigned to Maryvillia as revised in this study (see discussion above). Protillaenus is based on poorly preserved material (e.g., Shaw 1952, pl. 57, figs 14, 15), and the name is best restricted to the types.

Figures

FIGURE 2. Phylogenetic analysis of Blountia and related taxa. 1. Strict consensus of six trees of length 30 (CI, 0.50; RI, 0.62; RC, 0.31). Names of species from Steptoean strata are identified by bold font. 2. Optimized character distribution plotted on one of the most parsimonious trees. Only unambiguous transformations (i.e., optimize to the same nodes under the assumptions of ACCTRAN and DELTRAN) are shown; open circles indicate characters that are homoplastic. Numbers above the circles refer to characters and those below identify particular states (Table 2).