The hypostoma has a transversally triangular form, and is divided only in two fields through a shallow semicircular groove near the posterior margin. The two maculæ are situated above the groove near its superior sinuses. They are elongated, fig. 17, elliptic with the narrow pointed end directed outwards and the broad rounded end inwards. The chief surface is scooped out as a shallow depression. The granulated spot is situated on the broader end and covering it completely. The relatively large lenses are arranged in five regular rows, the uppermost one being the longest. On the interior surface of the hypostoma there are the corresponding sockets of both maculæ with smooth surface. The horizontal sections of the granules figs. 18, 19 present the image of white rings in close contact, without, however, to occasion a prismatic structure, a dark interspace lying between each ring. These lenses are filled with a dark mass, and in some the same sort of radiated structure is perceptible as in the lenses of the cephalic eye. In horizontal sections of the cephalic eye the lenses approach the polyedral shape. In another section near to the surface of another specimen the lenses are decidedly hexaedral. The vertical sections, fig. 14, reveal their real nature as lenses where they lie as a string of beads with a dark nucleus enclosed within a thin whitish shell. They are covered by a thin membranous lining. When seen in transmitted light the lenses proper are dark, and the shell white and in reflected light the lenses are lighter than the rest. =Br. laticauda= ANGEL. Pl. II figs. 6-13. Lower Silurian from Dalecarlia. The hypostoma, f. 10, is of a broad clypeate shape, the anterior margin rounded without any large projecting wings. On the exterior surface there are two grooves parallel with the rounded inferior margin. As in Br. polyactin the two elliptic tubercles are situated on the inferior edge or slope of the upper groove and they are deepened by a shallow depression as in Br. platyactin. The granulated spot situated along the posterior margin of the macula deviates much in shape from that of the other species. It consists of a long and narrow stripe ending in a fine point outwards and widening inwards, where it is rounded, forming thus a claviform, curved elevation. Around the granulated area the maculæ are quite smooth, and show in a horizontal section an irregular structure of tiny black dots nearly resembling the structure of the hypostomic shell. We have not been able to obtain any good vertical section, but by casts of the interior side of the tubercles it is found that the granules form polyedric facets like those of the eyes though perhaps not so regular. There is a specimen with the granules intact, and the polyedric shape is then not so distinct.