The strange transverse, bipartite hypostoma carries the small, round, tuberculose maculæ on the superior moiety. As seen from the interior (fig. 53) they are obscurely maculate, but it is doubtful whether these black dots are derived from lenses, as the surrounding hypostomic surface also has the same mottled aspect. =Trochurus= sp. Pl. IV figs. 54, 55. This hypostoma belongs to an unknown species of Trochurus from the Southern Gotland (Burs). Its macula are placed almost as in the preceding species, but are much larger. They are surrounded by prominent margins. No lenses have been discovered on them. CONCLUSIONS. In reviewing the genera and species enumerated above, as to their number in which the structure of the macula has been observed, we arrive at the following results. ---+----------------+-----------+---------------------+ | | Number of | Number of species in| | Genera. | species | the maculæ of which| | | with | the structure has | | | maculæ. | been examined. | ---+----------------+-----------+---------------------+ 1 | Acaste | 1 | -- | 2 | Acidaspis | 1 ? | -- | 3 | Asaphus | 18 | 7 | 4 | Barrandia | 1 | -- | 5 | Bronteus | 9 | 5 | 6 | Bumastus | 7 | 1 | 7 | Calymmene | 4 | 2 | 8 | Centropleura | 1 | -- | 9 | Chasmops | 1 | -- | 10 | Chirurus | 9 | 2 | 11 | Ctenopyge? | 1 | -- | 12 | Dalmanites | 10 | 2 | 13 | Dysplanus | 2 | 2 | 14 | Encrinurus | 3 | 1 | 15 | Griffithides | 1 | -- | 16 | Herpes | 2 | -- | 17 | Harpina | 1 | -- | 18 | Holmia | 2 | -- | 19 | Homalonotus | 2 | 1 | 20 | Hysterolenus | 1 | -- | 21 | Illænus | 9 | 5 | 22 | Lichas | 4 | 1 | 23 | Megalaspides | 2 | -- | 24 | Megalaspis | 3 | 1 | 25 | Nileus | 2 | 2 | 26 | Niobe | 5 | 2 | 27 | Ogygia | 3 | -- | 28 | Paradoxides[42]| 8 | -- | 29 | Peltura | 1 | -- | 30 | Phacops | 3 | -- | 31 | Phaëtonides | 1 | -- |