KONGL. sv. VKT. AKADEMIENS IIANDU 



HAN I 



, 34 



s T :i i 



8 





Asaphus sp., probably A. rauiceps, Pompeckj, Trilobitcnfauna Ost- und Wcsl 

 Preussens, taf. VI, I'. 7. p. 80 an seinem Eiinterrande liegen zwei kleine, flachc Höcl 

 chen, (lic als Reste des Hinterlappens aufzufassen sind i 



<i< 



itail. 



We shall now describe the A.saphi which \ve have been able to examine more in 



isaphus expansus L. 



Pl. I tigs. 8—17. 



Iii the numerous specimens of which wc have examined the hypostorna, there are 

 always small, nearly circular maculae which h\ their lighter colour are marked ou1 from 

 the surrounding smooth space of the inferior sinus of the lateral grooves vvhere they are 

 situated. They do not rise at all above the surrounding surface from which thej are 

 separated onlj by ;i fine, scarcely perceptible line. On the interiör surface of the hypo 

 stoma they are better seen, and the enclosing line is deeper and more distinct. Their 

 surface i- there quite as smooth and even as on the exteriör side of the hypostorna. 

 Thev do not consequently in the least manner resemble muscular impressions as observable 

 on the inside of the glabella of other trilobites. These are on the contrary elevated above 

 the surface and finelv striated in various ways. 



The peculiar nature of these maculae i> revealed through the various sections wc 

 have made. In pl. I fig. 15 a vertical section across the entire hypostorna i- repre- 

 sented. The sectioned, dark niacuhc (a) lie on both sides of the faintly curved central 

 field, in the sinus of the lateral grooves. and the strongly developed terrace lines continue 

 sidewards just a little on the interiör side, where the duplicature tums round. As scen 

 in a magnified vertical section (fig. 16) the maculae consist of horizontal, whitish, straight 

 lines, probably lines of successive growth, and these are eros.sod rectangularly by more 

 irregular whitish lines separated from each other through dark spaces. The whole thus 

 gains the aspect of a dark surface cancellated by white lines. This retieulate<l or spongious 

 inacula is enclosed as to it-, superior as well as to its inferior part in the compact and 

 homogenous test of the hypostorna and oecluded from the influence of the light. It- 

 value as a visual organ consequently is insignificant. In a horizontal section (fig. 17) 

 the strueture is still more bewildering. There the whole macula is a confused, spongious 

 white mäss with dark spaces between the white meshes, and only at one side, the left one, 

 some obscure indications as of polygones are visible. It would indeed have been impossible 

 to interprete what this means, had not the study of the cephalic eye given a elue thereof. 



The eye of this species is covered with a delicate perfectly smooth and glossy in- 

 tegument (f. 12) which is reposing immediately on the prismatic lenses of the cornea. 

 In a few instances, depending on the colour or the sta te of preservation of that in- 

 tegument the lenses are indistinctly translucent. Owing to their state of preservation 

 their aspect is greatly variable. They are in many instances, as seen in tig. 9, six- 

 sided or some rhombic, foursided or even quadratic (f. 8, 10). They are all of 

 the same length, 0,2 min. along the surface proper of the eye, but are lengmened to 

 0,3 inni. towards the horder of the eyes, f. 1*2, which will be described further on; 



