Glassification and phylogeny of the trilobite order Lichida

Abstract

The Lichida (informal lichide) comprises two families: the Lichidae (informal lichid) and Lichakephalidae (= Eoacidaspididae). A new interpretation of lichide glabellar morphology is given, based on ontogenetic data and comparative morphology of holaspides. No occipital lobe is developed but, in front of the occipital ring, L1 is divided into subsidiary lobes L1a and L1b. The large (bullar) lobe typically lying anterior to L1b originates from L2 fairly early in ontogeny and later expands forwards, apparently incorporating more anterior parts of the glabella as it does so. L1a, L1b and the bullar lobes may be variously fused with each other or with the fixigena. The Lichakephalidae certainly includes 4 genera, 2 further genera (1 new) being: included there with reservation, whereas 43 genera and subgenera (5 new) are recognized within the five subfamilies of the Lichidae. New diagnoses are given for all these taxa with a summary of their geographical and stratigraphical distribution and lists of the species included in each genus. The phylogeny of the Lichida is discussed and cladograms summarize the relationships of genera within each subfamily. The Lichida may be related to the Odontopleurida and may also have more distant affinities with the Scutelluina.