The clypeiform hypostoma is divided in two fields, one anterior larger, in the centre elevated in a short, blunt knob, and a posterior, bearing the two elevated rounded maculæ, just below the semicircular groove which separates it from the anterior field. These fields are surrounded by a large border which is posteriorly emarginated through a short rounded sinus. The surface is entirely covered by small semiglobular wartlets perforated by a straight pore or duct, which being filled with a black mineral, probably iron pyrites, gives a peculiar and characteristic aspect to the sections. In the same manner the whole mass of the hypostoma is pierced by straight, black lines, also filled up pores, starting from the outside and ending before attaining the inner surface. The maculæ are prominent, separated from the hypostoma through narrow, distinct grooves, ovate, with the pointed end directed obliquely outwards, against the margins of the hypostoma. They are covered with wartlets and leaving only a little oblong spot free, quite smooth, this being consequently the macula proper. But in a longitudinal section there is not the least distinction between this macula and the other hypostoma, only, that it is free of pores. =Calymmene tuberculata= BRÜNNICH. Pl. III figs. 8, 9. We have succeeded to prepare a horizontal section of the macula. This is oval, perfectly homogenous and without any structure proper, showing only indistinctly a mottled medley of pale, brownish spots in the clear mass. There is in both maculæ a small dark, angular spot placed in their inferior part, fig. 9. =Centropleura= ANGELIN. This author has delineated most distinct maculæ in Centr. Steenstrupi pl. III fig. 4, b. two, small elongate darkish spots, near the posterior margin. I have not seen any specimen of this trilobite and have consequently not been able to follow up ANGELIN'S observation. =Chasmops= M'COY. Pl. III fig. 10. In his work on the Russian Phacopidæ FRIEDR. SCHMIDT has given the figures of Chasmops Eichwaldi and Ch. Wesenbergensis showing, as it were, patches of black maculæ. But as there is no mention of them, and as they are quite unlike the macula? which are described here, I am in doubt of their real nature. We have figured a macula from the hypostoma of a Chasmops, probably Ch. macroura, from a drift block near Rostock. It is elongate and narrow, more than four times longer than broad. Its smooth surface is a little scooped out and no structure is observable. =Chirurus= BEYRICH. We find the hypostomic maculæ annotated and delineated as occurring in the following species. _Ch. bimucronatus_ SALTER pl. 5, fig. 5 as two narrow elongated pits, surface seems intact. No mention of them in the letter-press. _Ch. exsul_ SCHMIDT pl. VI fig. 9. Indications of the oblong, narrow maculæ. _Ch. macrophthalmus_ SCHM. pl. VII, figs. 1 c, 2. Faint indications of narrow pits.