The buckler in its contour resembles very much the head of the I. gigas; it is, however, rather more rounded before, and arcuated behind. The oculiferous tubercles, are very peculiar, being very large, round, and exceedingly prominent. They have a good deal the appearance of solid hemispheres placed on the forehead of the animal. They are exactly on a line with the two abdominal furrows. The abdomen is composed of eight distinct articulations; the middle lobe is rather larger than the lateral lobes. The tail is suborbicular, convex, and rather less than the head. Length nearly five inches. Breadth almost three inches. This magnificent Isotelus was obtained near Trenton Falls, in New York, by P. A. Browne, Esq., and now forms a part of his fine collection of fossils, in this city. It occurs in black transition limestone. It differs essentially from the I. gigas of Dekay, in the magnitude, collocation, and contour of the eyes. Those of the I. gigas are oblong and lunate, and nearly half the distance between the anterior and the posterior edges of the buckler; those of the I. Megalops are not only much larger, but they are round, and very near the posterior border of the head. Isotelus Stegops.[41] Green. Casts Nos. 26 and 27. [Footnote 41: From two Greek words, which signify "covered eyes."] Clypeo antice, caudaque postice attenuatis; cute coreacea punctis minimis. The head of this species is nearly in the form of a spherical triangle; its anterior edge is vertically flattened all round, but does not produce a narrow raised rim, such as is described by Dr. Dekay, to belong to the I. gigas. The eyes are prominent, and rather nearer the lateral edge of the buckler, than to its posterior border. The shell of the buckler forms a remarkable projection over the top of each oculiferous tubercle, something like an eye-lid. Continuous with the edge of this cuticular projection, there is a curved linear depression, which terminates on both sides, at the edge of the buckler. This kind of suture, though remarkably developed in this species, is not peculiar to it, being more or less distinct in most of the Isoteli. The articulations of the abdomen are lost; there can be little doubt, however, that they were eight in number. The tail is subtriangular, and less in magnitude than the buckler.