Middle Ordovician (Darriwilian) cheirurid trilobites from the Table Cove Formation, western Newfoundland, Canada Author Adrain, Jonathan M. 0000-0002-7000-1311 jonathan-adrain@uiowa.edu Author Pérez-Peris, Francesc 0000-0002-7000-1311 jonathan-adrain@uiowa.edu text Zootaxa 2021 2021-09-24 5041 1 1 73 http://dx.doi.org/10.11646/zootaxa.5041.1.1 journal article 10.11646/zootaxa.5041.1.1 1175-5326 5531880 5E82BE60-609F-4287-AC67-D86536FB7686 Mainbrookia n. gen. Type species. Mainbrookia becki n. sp. , from the Table Cove Formation (Darriwilian), western Newfoundland , Canada (Laurentia) . Other species. Sphaerocoryphe akimbo Tripp, 1967 , Stinchar Limestone Formation (Darriwilian), South Ayrshire , Scotland (Laurentian-affinity Midland Valley Terrane); Sphaerocoryphe saba Tripp, 1962 , Confinis Formation (Darriwilian), South Ayrshire , Scotland (Laurentian-affinity Midland Valley Terrane). In addition, provisionally assigned are remaining poorly known Laurentian-affinity forms from the Darriwilian. From the Confinis Formation (Darriwilian), South Ayrshire , Scotland (Laurentian-affinity Midland Valley Terrane): Sphaerocoryphe sp. A of Tripp (1962 , p. 21), Sphaerocoryphe sp. B of Tripp (1962 , p. 22), Sphaerocoryphe sp. C of Tripp (1962 , p. 22). From the Stinchar Limestone Formation (Darriwilian), South Ayrshire , Scotland (Laurentian-affinity Midland Valley Terrane): Sphaerocoryphe sp. A of Tripp (1967 , p. 66), Sphaerocoryphe sp. B of Tripp (1967 , p. 66), Sphaerocoryphe sp. of Tripp (1979 , p. 350). Etymology. After the town of Main Brook, which is near to the locality from which the type species was collected. Gender is feminine. Diagnosis. Cranidial fixigenal lateral border spine present; pygidium with three axial rings and three pairs of spines, first pair large, elongate, and dorsally produced. Discussion. The assigned Scottish species are somewhat difficult to fully interpret, as they are all based on coarsely preserved internal mold material illustrated with very small photographs. Nevertheless, M. akimbo has a pygidium with essentially the same morphology as that of M. becki ( Tripp, 1967 , pl. 4, figs 8, 9) and it definitely has a fixigenal lateral border spine ( Tripp, 1967 , pl. 4, fig. 4). Mainbrookia saba is not known from the pygidium, but definitely has a fixigenal lateral border spine ( Tripp, 1962 , pl. 3, fig. 11). The remaining open nomenclature Darriwilian Scottish species are largely scraps that lack evidence of diagnostic features. We assign them provisionally to Mainbrookia , but obviously this should be revisited if more information becomes available.