This restoration gives to the proprietor of this cephalon a length of nearly 20 inches. The figure does not however do full justice to the proportions of the animal. In the cephalon which has served as a base for the restoration the great ovoid central lobe of the glabella has a length of 2¼ inches. Mr BILLINGS speaks of a specimen of _Lichas superbus_ in which the length of this lobe was fully 3 inches. If the increase in size of this part was accompanied by the same relative increase in the size of the entire animal (and there is no good reason for assuming the contrary), such a fragment would represent an individual fully 24 inches in length, a size unsurpassed and unequaled by any other known trilobite. With his extravagant armor of defense and aggression, _Terataspis grandis_ must have been easy lord of his invertebrate domain and no very palatable morsel for the heavily plated fishes of his day. In the genera PHACOPS and PROETUS great size was never attained. The earlier forms of both of these genera were of inconspicuous proportions and their maximum size was attained in the middle Devonian. An entire _Phacops rana_ is figured in the Palæontology of New York, Volume VII, which has a length of 4 inches, and cephala in the Museum collection indicate an original length of 5 inches, perhaps the greatest size which has been observed in this genus. PROETUS has a still smaller habit, that is, its maximum size is never so great, and, probably, the largest example of the genus recorded is represented by a cephalon of _Proetus macrocephalus_ from the Hamilton group, which belonged to an individual fully 3¾ inches in length. [Illustration: Plate V] * * * * * Transcriber Note The above article was published as part of the "Tenth Annual Report of the State Geologist For the Year 1890." (Albany, NY) on pp. 87-90 and Plate V with "Explanation of Plate V" on facing page. It was also published as part of the "Forty-fourth Annual Report of the Regents for the Year 1890" (Albany, NY) on pp. 111-114 and Plate V. Unfortunately, the available scans of these documents DO NOT include the Plate nor the Explanation pages.