Megal. attenuata Wahlenberg.

[Pl. V figs. 1-6.]

The long and narrow maculæ are crescent-shaped and project beyond the hypostoma supported on the superior surface of a sharp extenuated edge where they rest as on a shelf. They consist, as seen in vertical sections, [figs. 5, 6], of alternating rows of light and black streaks, and in a horizontal section the spongious network appears, as it is found in Asaphus and others and thus indicating the tendency of this organ to assume a prismatic structure though undeveloped.

The cephalic eyes in M. attenuata form the most regular hexaedral prisms [fig. 1 a], short and covered by a thin cornea. The border zone of the eyes has a structure exactly like that of the maculæ, the same as in the spongious zone of Asaphus.

Megal. limbata Boeck.

[Pl. V fig. 7.]

We give a new figure of Brögger's original specimens, as his figure 23, Tab. II is incomplete and incorrect. The maculæ are situated a little higher up on the sides of the central gibbosity.

Megal. planilimbata Ang.

[Pl. V fig. 8.]

The maculæ are crescent-shaped and not so prominent as in Meg. attenuata and the visual spot in the same position as there.