Asaphus Brongn.
The wellknown hypostoma of this genus has the same characteristic shape, though more pronounced, as in Ptychopyge, with its posterior margin deeply indented, so as to form two large, pointed lobes. There is properly only one median field, surrounded by flat, lateral borders, continuing down into the posterior lobes, from which it is separated through a shallow groove. The macula are situated in this groove, on each side of the inferior border of the central field. They are more or less prominent, but whatever their form may be, their surface is always entirely smooth, lying well circumscribed amidst the surrounding terrace lines.
The following list enumerates all the species in this genus, of which previous authors have delineated the tubercles, though they in the descriptions only in very few instances have mentioned their presence.
A. acuminatus Nieczkowski, »Zusätze zur Monogr. der Trilobiten 1859», tab. I, f. 6. Maculæ most prominent, but no mention made of them in the description.
A. (Isotelus) canalis J. Hall, Pal. N. Y. I, pl. 4 bis, f. 18-19. Though this and a following species probably on account of the deviating conformation of their body, belong to a different genus or subgenus, I mention them along with the Asaphi, as there is the greatest similarity in their hypostoma. Fragment of an interior cast; still more strange is the fragment showing part of the interior surface and the duplicature.
A. expansus L. Br. I pl. VII f. 3, BR. II pl. I f. 2, 2 c. In the two first figures there are no tubercles nor maculæ marked, in the last figure there are distinct tubercles.
A. fallax A. pl. XXVIII f. 3, c. BR. II pl. I, f. 3, both nearly congruent.
A. (Isotelus) gigas J. Hall, Pal. N. Y. 1, pl. 60, f. 7 g, pl. 66 f. 5, the inside of an entire, uncommonly large hypostoma gives a general good view with the macula; which are large and evident. He mentions the maculæ as »two circular spots». »These probably indicate the points for the attachment of muscles and tendons upon the inside,» he adds.
A. ingens Barr. Novák II, pl. I, f. 7, a good figure showing two semiglobular maculæ. Barrande's figures pl. 33, f. 7, 8 are not distinct.
A. ludibundus Tqt. Br. II, pl. 1, f. 7. Two semilunar sulci on the cast of the interior surface, being only the posterior borders of the maculæ which are a little more raised and distinct than the rest.