There are some indistinct indications of maculæ in several of the hypostomas figured in Barrande's Système pl. 15.
Proet. signatus Lindstr., Gotl. Trilob. Pl. XV fig. 17, shows very distinctly the two maculæ.
Proet. concinnus Dalm.
In this, as well as in the few other species of Proetus which we have studied, there is that peculiarity of the surface of the hypostoma that two more or less distinct ridges form an acute angle just below the faintly arcuated anterior border. The terrace lines are exactly alike those of the Phillipsiæ, only visible on the central field and ceasing just above the maculæ, where there is a transverse smooth field. The posterior margin has two pair of very short points, one on each side. The macula are lengthened tubercles, somewhat bent and have an oblique position. They are surrounded by tiny prickles and as seen in [fig. 23] the macula proper forms a white, elliptic spot on the tubercle. The cephalic eyes are lengthened prisms covered by a thick membrane. They are convex at their base and in a transverse section they show a radiate structure of their interior.
Proet. conspersus Angelin.
We have figured a decorticated hypostoma with impressions of two reniform maculæ. The vertical sections of the cephalic eyes show a thin stratum where the lenses are much shorter than in the previous species and covered by a thin film of the common test. The same is also the case in a species which probably is Proet. verrucosus.
Proet. signatus Lindström.