In another, undetermined Bumastus ([pl. II figs. 47, 48])[40] the hypostoma (from Klints, Othem, isle of Gotland) is of a more elongate obovate form, the anterior margin elevated, rounded, the terrace lines faint, the tubercles are larger than in the former Bumasti, oblong, curved, beanshaped, evenly rounded and smooth.
[40] Probably the same as Bum. sulcatus pl. XII fig. 12 in my paper on the Trilobites of Gotland 1885.
Another of the new species is one that Liljevall has found at Korpklint near Wisby ([Pl. II figs. 41-46]). The hypostoma is more elongate than transverse with the anterior margin regularly arcuated, by far not so prominent as in B. sulcatus and the former. By a shallow groove the exterior surface is divided in two fields, the anterior one the largest and covered with a few, distantiated, concentric terrace lines. The posterior field is smooth, nearly even and the maculæ lie just in the groove, with their axis oblique to the longitudinal axis of the hypostoma, beanshaped and smooth. The cephalic eyes show in a horizontal section hexaedral white walls enclosing a dark space in which some indistinct radii emanate, [fig. 41 a]. In the vertical sections the prisms are narrow and elongate and the integument by far not so thick as in Bumastus sulcatus, [fig. 42, 43]. The border zone of the eye in this ([fig. 41]) as well as in B. sulcatus, as seen in horizontal sections, agrees with that of the Asaphidæ.
Bumastus sp. inlet.
In a detached piece of limestone, found in Gotland, at Norderstrand, near Wisby, two hypostomas and a free cheek lay embedded along with a coral of the genus Acantholithus and a Bronteus probably belonging to a new species. As the coral has not been found above the uppermost beds of the Lower Silurian it is probable that the trilobites also are derived from the same horizon.
The hypostoma, figured [pl. III fig. 1], is broadly tongueshaped, with a short, blunt, triangular wing on each side of the anterior margin. The exterior side is nearly completely occupied by a single large field, which is convex and decorated by sparse terrace lines. Below this a smooth, nearly even plane, reaching to the inferior, elevated border of the hypostoma. The two tubercular macula' are situated exactly on the boundary line between the convex and the plane field. They are elongately ovate, pointed outwards, rounded inwards, with smooth and glossy surface. That portion, on which in the species of Bronteus the granular spot rests, is transversally wrinkled by some faintly elevated, sigmoid lines ([fig. 2]). It would have been of great interest to investigate the interior structure of these curious maculæ, but the scarcity of the material has prevented our doing so.
The other hypostoma, [pl. III fig. 3-5], is larger and has the terrace lines more distantiated and forming more open curves, but for the rest it is of the same shape as the smaller, so that we may not ascribe these small deviations to a specific difference. The maculæ are more elongated, narrow, curved tubercles, thus differing from the next preceding. A section running through its left tubercle does not show any structure, but the shell of the maculæ is extremely thin, thus contrasting strongly with the surrounding thicker shell, [fig. 4 a]. The cephalic eye, again, remaining on the free cheek found in the same piece of limestone and probably belonging to the same specimen, has its surface well preserved and exhibits semiglobular lenses in low relief, [fig. 5].
Calymmene Brongn.
In the following species of this genus hypostomic tubercles have formerly been recorded.