Article: On Cephalaspis lyelli Agassiz

The type specimen of Cephalaspis lyelli, the genotype of Cephalaspis, has never been fully described nor properly figured, and its counterpart has hitherto been completely ignored. Both parts of the specimen have been further developed, especially the counterpart, and are here described in detail. The position of the species in Stensio's proposed new classification is established on the form of the oralo-branchial chamber. No other specimen of this species is known.