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Published online by Cambridge University Press: 01 May 2009
We have now finished the survey of the characters of the head-shield of Trinucleus sufficiently to enable us to discuss the vexed questions of the affinities, systematic position, and evolution of the genus; and from the foregoing details of the various species we can perceive that there are many difficult problems presented when we attempt to correlate its structure with that of other trilobites. Whether the peculiar characters of the genus are the result of degeneration or of the persistent retention of early phylogenetic stages or of a reversion to such stages is a matter of dispute.
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