Illænus Roemeri Vollborth.
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.]
As the hypostomas in this genus generally are found detached it is often difficult to decide to which species they have belonged. So it is with that delineated in [Pl. IV] fig. 44 natural size. The two maculæ are situated near the centre of the hypostoma, just below the grooves which surround the large, globular disc. They are sunk in a little cavity, rounded and entirely covered by globular lenses ([pl. IV fig. 46]).
In another detached hypostoma of an unknown species the macula is smaller and the few lenticular globules larger than in the other, [fig. 48].
Lichas latifrons Angelin.