O. dilatata var. Sarsi Ang.
The hypostoma is in so far deviating that the terrace lines have a nearly vertical direction and in this respect much resemble those of the Phillipsiæ and the Proeti. The maculæ, near the exterior angles of the border groove are pear- or spoon-shaped with the apex directed downwards and outwards, and in consequence the longitudinal axis quite opposite to that of the usual direction. The surface is smooth, a little concave. No structure has been discovered. From the pointed apex a slightly elevated ridge runs along the posterior border of the hypostoma and joins the apex of the other macula.
Paradoxides Brongn.
The oldest record of any hypostoma at all amongst the trilobites is that given by Wahlenberg in his Petref. Suecana (1818) p. 37 Tab. 1, fig. 6, which he, however, considered as the head of the trilobite which he named Entomostracites bucephalus. Figures with maculæ have been given of
Par. Davidis Salter Mem. Geol. Survey Dec. XI pl. X, fig. 3, a fine figure of a hypostoma with two large oblique maculæ. Linnarsson in »de undre Paradoxideslagren vid Andrarum» pl. II fig. 2 delineates a gigantic hypostoma with two crescentic tubercular maculæ, having 10 mms. in length.
Par. Forchhammeri Angelin Pl. II fig. 3. Brögger, Paradoxidesskiffr. vid Krækling tab. II fig. 10 two marks somewhat different from Angelin's figure. Linnarsson 1. c. pl. I figs. 9, 10 two hypostomas with maculæ.
Par. Tessini, var. Wahlenbergi Angel. Pl. I a, fig. 1 b.
Par. Tessini, var. oelandicus Ang. Tab. I a, fig. 2 b. Angelin's figure of this hypostoma is incomplete in so far that he had not found the peculiar falciform horns on both sides of the posterior border. Pl. V, fig. 33.
Par. rugulosus Corda has, according to Brögger, Krækling, pl. II fig. 2 two long, straight callosities, probably corresponding to the maculæ in other Paradoxidæ.