The vertical section of the hypostomic eyes fig. 33 shows in their present changed condition an evident longitudinal direction of the chief elements, quite as the lenses of the eyes. But in how far there ever has existed such prismatic lenses, now changed, we have no evidence definitely to ascertain, but the probability seems to be great that this was the case. =Illænus gigas= HOLM. Pl. IV figs. 34-37. The maculæ in this as well as the other Illæni are so faintly elevated and so inconspicuous that the greatest attention is needed to find them. The maculæ are elongated, narrow, elliptic on the same level and parallel with the straight anterior margin of the hypostoma. A cast of the left macula is pitted by numerous marks of the lenticular globules of the surface, fig. 37. In the cephalic eye the prisms are seen translucent beneath the cornea. Near the superior border they are larger, fig. 34, almost the double size of those near the inferior border, fig. 35. =Illænus sphæricus= HOLM. Pl. IV figs. 42, 43. Comes near to the previous species. The globules on the surface of the elliptic maculæ are not, however, spread over the entire macula, leaving only a narrow border all around free. The lenses in the cephalic eyes fig. 42 are globular as seen on the surface, alike those of the maculæ. =Illænus Roemeri= VOLLBORTH. Pl. IV figs. 38-41. The maculæ lie on elevated tubercles and are of a strange shape, being sharpely pointed outwards, rounded inwards. That in fig. 39 is still more peculiar with a narrow stripe on the interior and upper margin. The lenses are larger and more distinct than in any other species of this genus. Beside the species now mentioned we have also observed hypostomas with maculæ in Illænus laticlavius EICHWALD from Estland, in Illænus Linnarssoni HOLM, and in an unnamed species from Dalecarlia figured without macula by Dr. HOLM in his memoir on the Illænidæ pl. III fig. 22. We have not seen any lenses on the maculæ of these three lenses. =Lichas= DALMAN. We have not been able to find any notice about the exceptional maculæ of this genus. There is only a figure of the hypostoma of Lichas hylæus HALL Pal. of N. York vol. VII pl. XXV fig. 5 which would seem to show a pair of narrow, oblique maculæ, but these are quite without resemblance with the maculæ of the true Lichas. The hypostoma of Lichas is of a characteristic type, broad, with the incised posterior margin and its two lappets reminding of Asaphus, with its large rounded, faintly elevated median part near the anterior margin reminding of Illænus, as also do the lenticles of the maculæ. The maculæ are of a minimal size, scarcely 1 millim. in diameter and thence easily overlooked. Pl. IV figs. 46, 48.