Article: Evolution of the Silurian trilobite Tapinocalymene from the Wenlock of the Welsh Borderlands

Some calymenid trilobites from the Wenlock Series of the Welsh Borderland are described and assigned to a new genus Tapinocalymene, type species T. nodulosa (Shirley 1933). An evolutionary lineage from T. volsoriforma sp. nov. (early Wenlock) through T. vulpecula sp. nov. (late Wenlock) to T. nodulosa (late Wenlock) is proposed, involving an increase in the length and area of the preglabellar furrow. Tapinocalymene was probably benthic in habit, and occurs in somewhat offshore, generally deepish water, elastics. Calymene diademata Barrande, 1846 (Wenlock, Bohemia), C. nasuta Ulrich, 1879 (Llandovery, United States) and C. blumenbachii Brongniart, 1822 (Wenlock, England), respectively the type species of the calymenines Diacalymene Kegel, 1927, Spathacalymene Tillman, 1960, and Calymene Brongniart, 1822 are figured and compared with members of Tapinocalymene. S. nasuta and T. nodulosa both have a particularly long preglabellar area, but each differs in its form and derivation. Several Ordovician and Silurian calymenid genera, some only distantly related, evolved a long preglabellar area, the taxonomic value of which should be treated with caution.