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.
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.