_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. _A. nobilis_ BARR. pl. 32, f. 6. Indistinct traces of maculæ. In the figure 6, pl. 31 representing the hypostoma of a young specimen, there are no tubercles at all. If the figures were to be relied upon, it might be assumed, that the tubercles appear at a more mature age. _A. Powisii_ SALTER, pl. 23, f. 6. Two semilunar, narrow tubercular maculæ, their interior apices converging towards the anterior border of the hypostoma. _A. raniceps_ A., pl. XXVIII, f. 2 c., BR. II, pl. 1, f. 4. A good figure. _A. raniceps_ var. _maxima_ BR. II, pl. 1, f. 6. Semilunar impressions on a cast and thus far incomplete. _A. striatus_ BOECK. To this belongs probably A. expansus M. SARS »Ueber einige neue oder unvollständig bekannte Trilobiten» in Isis 1835 p. 333, and especially p. 340 and the following (Bemerkungen über die untere Seite von einigen Trilobiten). SARS there gives a very good description of the exterior side, where he also mentions the two maculæ, pl. IX, f. 9 a, b. (»2 kleine Knoten»), BR. I, pl. VIII, f. 4 a, and BR. II, pl. I, f. 9. These latter figures differ in so far, that the former has the maculæ excavated or rather tubular below, in the latter again they are regular. _A. trinucleorum_ BR. II, pl. I, f. 16 a large specimen with linear maculæ arranged rectangularly in respect to the longitudinal axis of the hypostoma and both on the same level.