Abstract

Morphology is reviewed with special reference to the doublure and thoracic characters; a reconstruction of Richterarges aquilonius is used to suggest possible lichid anatomy. The relatively large hypostome and wide doublure, and the thorax with, or without, the strongly convex posterior pleural bands characterize lichids, in addition to the distinctive glabellar morphology. Relatively shallow furrows on the external surface form strong ridges on the visceral surface of the exoskeleton; apodemes are absent. Type specimens of species described by Schmidt, recently traced in Russian museums, are figured. Lichids differ from odontopleurids in morphology and anatomy, and are unlike Scutelluinae; accepted subfamilial divisions of Lichidae are reinforced by thoracic characters. A single lichid species is known in the early Tremadoc, in the early Middle Ordovician the main four subfamilies are recognised and are widespread; their ancestry and early diversification remain unknown.

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