In a little group that has retained larval or ancestral characters during a great part of the palæozoic period, the genus Harpes stands as a type. It has ranged from the oldest Lower Silurian, if we join the related Harpides, to the middle Devonian. From near the top of the glabella, though not so much forward as the facial ridge of the blind trilobites (Olenus, Liostracus etc.) a straight ridge of much varying length stands out on both sides and at its extremity two or three globular stemmata with glossy surface lie encased. Probably this ridge has the same origin as in the Olenidæ, the more so, as there are indications of an extensive circulatory system. On plate IV fig. 18-19 the right hand ocelli of Harpes vittatus BARR. from Lochkow, Bohemia, are represented. They are two, lying isolated near each other, quite globular with circular outline, smooth and glossy as to exhibit a shining surface. Their size is 0,4 mm in diameter. Being cut vertically in the direction of the longitudinal axis of the head they resemble elongated hemispheres, convex on the exterior surface, slightly concave on the interior. The test of the head lies between them as a saddle and covers them only partially and on the outer sides they lie with their margins encased in the head shield. Seen in thin sections of the right lens and magnified the whitish mass is traversed by vertical, blacker streaks, standing somewhat radiating towards the sides and cancellate. The other lens has a horizontal row of black dots. All this is probably not of any structural value, only due to later changes. The remarkable genus Harpides from the lowest Lower Silurian belongs also to this group and has beside the fixed peduncle a peculiar elongated ridge going from the eyes to the lateral margins of the head[33], a ridge which is also present in some of the true Harpes. [Footnote 33: Harpides breviceps cannot belong to this genus and is rather related to Erinnys SALTER, as also MATTHEW holds it.]