At first we must point out a certain resemblance which prevails between the hypostomas and maculæ in Bumastus and Bronteus. Compare for instance Bum. sulcatus with Br. platyactin and Br. laticauda. The general form is nearly the same in both and the shape of the maculæ almost identical but for the complete want of granulations on those of Bumastus. To this resemblance must be added that there are, as known, forms of trilobites which by some authors have been regarded as Brontei and by others, again, ranked amongst the Illænidæ. Three species of Bumastus have been recorded as found in the Gotland strata, but of one of these no hypostoma is known. Besides, to judge by the head shields and hypostoma, there are a few new species. To begin with the most common =B. sulcatus= LDM. Pl. II figs. 33-40. The hypostoma is broadly shield-formed and the anterior margin is most characteristic being in its central part elongated in a short evenly rounded projection. The side wings are triangular acuminate, bent a little backwards and towards the interior surface. There is only a single rounded field passing into an evenly bent border, in front of which the projecting, elliptic maculæ lie. A second pair of wings stretches backwards near the posterior margin. We have not obtained any sections of the maculæ. The cephalic eyes figs. 36-38 are covered with an uncommonly thick stratum of homogenous shell, one and a half times as thick as the subjacent lenses. These are comparatively broad, above passing indistinctly in the covering stratum, below, at their basis, convex. In a horizontal section figs. 33, 34 they exhibit the common hexaedral or pentaedric aspect, their exterior sides being white and confluent without any separating lines. Their interior is dark and from the polygonal sides white lines go in giving the whole the appearance as of a starry, composite coral with its septa. The correspondence in structure with Bronteus laticauda pl. II fig. 7 is striking. A narrow space separates the surface of the eye from a nearly similar patch below the eve on the cheek 35 _b_, 38 _b_. But there the position of the composing strata is singularly reversed and the spongious or pseudo-prismatic stratum lies close to the outside and the homogenous stratum on the inside. The white longitudinal lines are well marked out and regular in the vertical section, fig. 38 _b_, indicating the prismatic structure most clearly. =B. barriensis= MURCH. Pl. II figs. 31, 32.