In the second faunas great Asaphids were not uncommon. As early as 1839 Dr. JOHN LOCKE described in the report of the Geological Survey of Ohio, a portion of an immense pygidium to which he gave the name _Isotelus maximus_. In 1843 Dr. LOCKE figured an entire individual of what he considered the same species, changing the name, however, to _Isotelus megistus_. This specimen measured nine and three-quarters inches in length. The figure was accompanied by outlines of two large pygidia, the greater of which was that referred to in 1839, which, the author says, coincided "with the end of an ellipse 22 inches long and 12 inches broad." This is an evidently much compressed fragment, measuring seven inches in its greatest transverse diameter, and assuming this as the greatest diameter of the pygidium and restoring the length from the proportions of the animal as there given, the original length of its owner would have been about 13 inches. The plate is incomplete on its anterior portion, and it is probable that the error in this estimate due to the exaggeration of size from compression of the shield, is compensated by the loss of diameter from imperfect retention. This great pygidium, with other large fragments of the same species, were used as a basis for a well-known restoration in plaster to be found in some of the older museums of this country. ANGELIN has given a restoration of _Megalaspis heros_ 14 inches in length and BRÖGGER estimated the original length of _Megalaspis acuticauda_ to be fully 16 inches. BARRANDE figured an entire _Asaphus nobilis_ from Etage D which measures 10½ inches.