D. centrotus Dalm.
This species has the maculæ placed near the posterior border, in a semilunar flat, devoid of the terrace-lines. The maculæ are elongated tubercles and do not show any structure when sectioned. The cephalic eyes have a thin membrane covering the short cupshaped lenses, which, closely packed, in the transverse section give the usual polygonal mosaic of hexaeders. They have a radiate structure, when decayed.
D. ladogensis Holm.
A specimen from Öland has the maculæ lying in the large field of terrace lines above the smooth zone at the posterior margin of the hypostoma. They are larger than in the former species, pearshaped, smooth and no structure visible.
Encrinurus Emmr.
I cannot find any former figure indicating the maculæ of the hypostoma in this genus than the only one of Angelin, Pal. Scand. pl. IV fig. 6.
As to the shape of the singularly formed hypostoma in the three Swedish species Encr. punctatus, obtusus and lævis we have found the anterior border so characteristic in them that it is sufficient to distinguish them from each other and to annul the doubts concerning the distinction of Encr. lævis from Encr. punctatus. We therefore in [pl. IV figs. 12-17] give the anterior margins of these three species, along with the profiles.
Encrin. punctatus Wahlenberg.