62 LINDSTRÖM, VISUAL ORGANS OF TIIE TRILOMTES. 



Nileus armadillo Dalm. 

 Pl. V figs. 10—15. 



There is some variability in the hypostoma of specimens from different localities. 

 The most known and numerous specimens are from the renowncd localities of Östergöt- 

 land. They are decidedly transverse, the proportion of the hight to breadth is as 3 to 5 

 and the narrow börder rims all round. In specimens from Kongslena, Västergötland, the 

 proportion is as 15 to "22, in specimens from Sandvik, Oland, again, we have 13 to 23 

 or 6 to 11. The maculae, fig. 14, are oblong, inwardly pointed, quite smooth, with a 

 little concavity in their centre, and their surface is slanting obliquely towards the sur- 

 face of the hypostoma, almost as in Niobe. There is no trace of any structure. 



The cephalic eyes are covered by a comparatively thiek membrane, a direct eon- 

 tinuätion of the general test, tig. 12, hiding a row of prismatic lenses. In some speci- 

 mens elongate, clear, crystalline rods eontinne downwards from the bases of the lenses 

 and are probably nothing but inorganic crystals of caleareous spar, tig. 11. — The eyes 

 are larger comparatively than in other species. 



Nilens (Symphysuriis) palpebrosus Dalman. 



Pl. V tigs. K'»— 18. 



As to its general form the hypostoma resembles that of the preceding species, but 

 there is no börder line, which is so characteristic to the former. The maculae have the 

 same form and are likewise situated on the median line. The cephalic eyes have pris- 

 matic lenses with much convex bases, in a transverse section they are hexaedral and of 

 interna! radiate strncture. 



Niobe Angelin. 



The following figurés have formerly been given of its hypostoma- with maculae. 



N. emarginula Br. II tab. 2 fig. 33. 



N. eajjlanata Br. II tab. 2 fig. 35. 



N. frontalis Br. II fig. 37. 



A T . insignis Br. I tab. IV fig. 1 d, II tab. 2 fig. 28. 



N. Iceviceps Br. II pl. 2 fig. 34. 



The maculae are distinguished from all other sorts of maculse, excepting those of 

 Mrgalaspis, in being, as it were, shelved on a sort of support, formed through the bulg- 

 ing of the hypostomic surface just below them, one such console for each. Their surface 

 lies eonsequently almost rectangularly to the adjoining surface of the hypostoma. They 

 are whitc and smooth. 



