KONGL. SV. VET. AKADEMIEN8 HANDLINGAR. BAND 34. N:0 8. 55 



from Dudley, fig. 47. The granules of the surface are larger and more rare between 

 the oeelli than for instance in Dalm. imbricatulus. Small lenses, undeveloped as Salteb 

 calls them, may in fact only be such granules of somewhat larger size than usual. Lenses 

 having the appearance as in Salter's fig. 6, as if a covering was partially destroyed and 

 the lens visible below it, I have also found in Swedish specimens, as represented in fig. 

 17. In a vertical section, fiir. 50, ;i delicate covering integument i- seen and the oval 

 lenses lie regularly vvith their frames around them quite as in Dalmanites obtusus and 

 in horizontnl seetions, lins. |s, 49, there are also the same sort of black, irregular döts, 

 being the sectioned tubes of the surface between the lenses. Bu1 in another feature there 

 is great interest. Beneath each lens there are fascicules of tiny rods, twice as long as 

 the lenses. They are represented in a vertical section in fig. 50 and in a tangential sec- 

 tion in fig. 19. 



As our imperfect knowledge of so delicate anatomical structures in fossil crustaceans 

 does not admit of secure comparisons with the visual organs of recenl crustaceans, no 

 suggestion can be given to interpret their nature. Probably they have do connection 

 with the structure of the eyes and it is not even certain that they are of organic origin. 



Dysplanus Burm. 



If there were no other characters to distinguish this genus from Ilhenus its strangely 

 deviating hypostoma must do it. We have examined two species and in both the hypo- 

 stoma is almost oval, evenly rounded both anteriorly and posteriorly. Near the anterior 

 börder two narrow, long hornlike wings project. They are flattened, thin and lameilar 

 from the basis and end in a hollow, acuminated point. 



]>. centrotus Dalm. 

 Pl. III figs. 53—56. 



This species has the maculae placed near the posterior börder, in a semilunar Ilat. 

 devoid of the terrace-lines. The maculae are elongated tubercles and do not show any 

 structure when sectioned. The cephalic eyes have a thin membrane covering the short 

 cupshaped lenses, which, closely packed, in the transverse section give the usual poly- 

 fona! mosaic of hexaeders. They have a radiate structure, when deeayed. 



D. ladogensis Holm. 



Pl. III figs. 57, 58. 



A specimen from Öland has the maculae lying in the large held of terrace lines 

 above the smooth zone at the posterior margin of the hypostoma. The}' are larger than 

 in the former species, pearshaped, smooth and no structure visible. 



