from the islet of Sandö, north of Gotland. Although we cannot give any account of its hypostoma, not having had sufficient material, the structure of the eyes is so peculiar that it seems worthy of being recorded. The integument is extremely thin and transparent and the subjacent lenses are clearly seen, and through their impact on the thin integument they make this to stand out in a very low relief above them (fig. 27). These lenses are uncommonly short, forming at the surface rather oblong, slightly hexaedral prisms with a narrow interspace between them. In a section lower down they have the shape of hollow, white rings filled with black mud and in a longitudinal section the white walls of the lenses look like short pointed spikes and interiorly they are completely empty. We here find also the same gradual change from regular cones to the spongious border zone as in the above mentioned species f. 29. The border zone is finely reticulated. =Asaphus (Isotelus) gigas= J. HALL. Pl. II figs. 1-3. The enormous hypostoma of this giant resembles in a high degree that of the Asaphi, but is at the same time the most evident verification of the experience that the hypostoma _per se_ cannot be regarded as the sole criterion for determinating the generic affinities of different species. The whole structure of this trilobite in other respects gives it a quite independent position, distinct, from Asaphus. We have had at our disposal several specimens of the large hypostoma, the dimensions of the largest, fragmentary in its anterior margin, being as follows: breadth 48 mm. length 41 mm., probably 47 mm. when entire, breadth of each of the posterior lobes at their bases 19 mm., length of the same 23 mm. The maculæ which are placed on the flat surface of the hypostoma without being at all elevated, are prominent through their great size and their pale, whitish colour. They are somewhat oblongue having their longest axis directed inwards and downwards. They attain a diameter of four millimeters. Horizontally sectioned, f. 2, they show the spongious texture and vertically the quasi prismatic reticulate structure richly developed, f. 3. The pillars are very distinct and continue without interruption all through the macula and in the interstices there are traverses joining between two pillars or partially filling the darkish interspaces, thus giving the whole the aspect of some »tabulate» coral sectioned. By the inspection of the horizontal section alone, presenting the irregular spongy texture it would have been impossible to imagine the ordinated arrangement which the vertical section reveals to us. The eyes consist of regular hexaedral prisms, and there is a very sharp boundary line between them and the spongious zone, which is very narrow and without distinct separating lines joins with the cephalic test. For the rest there are in all probability at least two different species sent from America under the name of Isotelus gigas, of which only the largest,