The hypostoma, figured pl. III fig. 1, is broadly tongueshaped, with a short, blunt, triangular wing on each side of the anterior margin. The exterior side is nearly completely occupied by a single large field, which is convex and decorated by sparse terrace lines. Below this a smooth, nearly even plane, reaching to the inferior, elevated border of the hypostoma. The two tubercular macula' are situated exactly on the boundary line between the convex and the plane field. They are elongately ovate, pointed outwards, rounded inwards, with smooth and glossy surface. That portion, on which in the species of Bronteus the granular spot rests, is transversally wrinkled by some faintly elevated, sigmoid lines (fig. 2). It would have been of great interest to investigate the interior structure of these curious maculæ, but the scarcity of the material has prevented our doing so. The other hypostoma, pl. III fig. 3-5, is larger and has the terrace lines more distantiated and forming more open curves, but for the rest it is of the same shape as the smaller, so that we may not ascribe these small deviations to a specific difference. The maculæ are more elongated, narrow, curved tubercles, thus differing from the next preceding. A section running through its left tubercle does not show any structure, but the shell of the maculæ is extremely thin, thus contrasting strongly with the surrounding thicker shell, fig. 4 _a_. The cephalic eye, again, remaining on the free cheek found in the same piece of limestone and probably belonging to the same specimen, has its surface well preserved and exhibits semiglobular lenses in low relief, fig. 5. =Calymmene= BRONGN. In the following species of this genus hypostomic tubercles have formerly been recorded. _Cal. Blumenbachi_ SALTER Monogr. pl. 8, fig. 9. The identity of the species is dubious. _Cal. duplicata_ SALTER Mon. pl. 9, fig. 22. The tubercles rather more linear and approximated than in the subsequent. SALTER calls them »two small transverse lobes ... forming a nearly continuous ridge». _Cal. tuberculata_ ANGEL. Tab. XIX fig. 5 c from the inside. It is remarkable that the eyes or that part of them where the cornea and the lenses should be found, has been destroyed and entirely lost in all specimens of the Calymmene known to us, many hundreds having been searched and every one with a lacuna on that spot. It must have been of an excessive thinness. We know only of one instance, the Bohemian Calym. Arago, in which BARRANDE has seen the eye intact and provided with a small number of about eleven sphærical lenses. =Calymmene intermedia= LDM. Pl. III figs. 6, 7.