The maculæ (fig. 14) are slightly concave, oblong, smooth, surrounded by comparatively large granulations. =Chirurus speciosus= DALM. Pl. IV fig. 1. The exterior surface of the hypostoma is sparingly covered by granules of larger size than in other Chiruri. The maculæ as seen in a cast are prominent near the posterior border, sunk in their centre and surrounded by a narrow distinct border line. In a horizontal section it as not been possible to detect any peculiar structure, only a dark border surrounding the interior clear surface. _Chirurus spinulosus_ NIECZKOWSKI. Pl. III fig. 15. We have had the interior surface of a hypostoma at our disposal from the lower Siluria, of Esthonia (Kuckers C^2) belonging to Dr. G. HOLM. The macula are well preserved, standing out black on the white surface, oblong, 1,5 millim. in greatest length (fig. 15). There are indications as of a great number of small lenses on these maculæ. Remarkable are the two elongated spots, almost 3 mm. in length, above these maculæ, of which already mention has been made under Ch. clavifrons. =Chirurus= sp. indet. Pl. III fig. 16. The hypostoma of an undescribed species from Öland. The maculæ are lengthened, ellipsoid and smooth tubercles lying in a groove. The finely granulated surface of the hypostoma shows rare smooth spots interspersed, being on the inside smooth pits, from which again in casts of the hypostoma larger tubercles are moulded. Of the same nature are those that are visible on the nucleus of Chir. speciosus and others. There are still some undescribed Lower Silurian species, for instance one nearly related to Ch. conformis with tubercular maculæ. A large hypostoma from the Leptæna limestone of Dalecarlia, 33 millim. in length, has a longitudinal macula, 2 millim. in length, as seen on the inside of the fragment. On pl. VI fig. 10 a little hypostoma is delineated that shows some resemblance with that of the Chirurus, but probably belongs to some other, unknown genus. It is Upper Silurian, found at Mulde in Fröjel, Gotland. It is of an elongated ovate shape, with the anterior border faintly arched, the anterior wings broad, truncate. A narrow elevated border surrounds the lateral and posterior margins. The somewhat vaulted surface is covered by fine granulations, and the macula, situated on equal distance from the anterior and posterior margins are ovate, smooth and directed obliquely inwards. There are two minute pointed processes on each side of the lateral borders and one on each side of the pointed posterior margin. =Ctenopyge= LINSN. =Ct. spectabilis= BR. (I, pl. XII, fig. 12 a).