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. Pl. IV fig. 49. The maculæ, seen in a thin section from the inside, are reticulate, fig. 49, or of a pattern exactly like that in the changed eyes or maculæ of Illænus and even Asaphus, and thus indicating that it was composed of short prismatic lenses. The vertical section of a macula of a specimen from another locality rather suggests the presence of large sphærical lenses than elongated prisms. The great thinness of the macula in contrast to the excessive thickness of the shell around the eye is seldom so evident as here. A specimen of an unknown species, found detached, has the macula? unlike the other species, oblique with the inferior end directed inwards, placed on the top of a sort of a little elevation, fig. 47. =Megalaspides= BRÖGGER. This author has a figure of M. dalecarlicus in II pl. 1 fig. 19 and also of an unnamed species fig. 20, both showing globular maculæ. In HOLM'S original description of his Megalaspis dalecarlicus (Trilobiten des Phyllograptusschiefers Dalecarliens figs. 8, 9) the same hypostoma is also figured. This genus seems to have a closer affinity with Ptychopyge than with Megalaspis. =Megalaspis= ANG. The following figures of hypostomas with maculæ have been published. _Megal. limbata_ by BRÖGGER I, tab. XII, fig. 10, and in II pl. 2, fig. 22, somewhat differing from the first figure. _Meg. planilimbata_ BRÖGGER II tab. 2 figs. 21, 21 a. Both figures incomplete and incorrect. The hypostoma has a large central ovate gibbosity with the maculæ near its basis, surrounded by the winglike expanded limbus. =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.