Article: Early Llandovery trilobites from Wales with notes on British Llandovery calymenids

Some early Llandovery (Silurian) trilobiles from Wales are described. The calymenids are compared with British Llandovery species, including two samples from Girvan, Scotland. Principal components analysis is used to demonstrate both the variation in profile of the preglabellar area and the independent and dimorphic (thus probably sexual) variation in relative glabellar width of Llandovery calymenids. Diacalymene crassa Shirley and D. marginata Shirley differ considerably from D. diademata (Barrande) in the profile of the preglabellar area and form the end of a spectrum of variation among British Llandovery calymenids: they are provisionally referred to Calymene s.l. Characterization of the genus Diacalymene in terms of 'ridging' of the preglabellar area is considered to be vitiated (at least for internal moulds) by the intraspecific variability of this feature and the subjectivity of its recognition. Two species are tentatively distinguished among Welsh early Llandovery calymenids, C. crassa and another species similar to a sample from Newlands, Girvan. Seven other species of trilobites are briefly described.