64 



lOHAN KIÆR. 



M.-N. Kl. 



breadth, i. e. not far from Holm's restored figure, which was drawn twice 

 natural size. The length of the body was about 76 mm. 



In my material there are also some quite small cranidiums of various 

 sizes, belonging to young stages and larval forms. These will be more 

 closely described in a special section. 



The following table shows more exactly the dimensions of 6 typical 

 cranidiums of various sizes. 



The Eye. 



Some few years ago the eyes were quite unknown as far as the 

 Mcsonacidae were concerned, and in his large work on the eyes of Trilo- 

 bites, L1NDSTRÖM ^ assumed that they lacked eyes on the upper side of the 

 cranidium. In his work on "Olenellus and other genera of the Mesonacidae" 

 Walcott thus describes the eye of a quite young specimen of Olenellus 

 Gilberti Meek. It is a cranidium of about 1.6 mm. in length, presumably 

 a nepionic stage of the species. Walcott writes: 



,,In one species I have been so fortunate as to find the outer faceted 

 surface preserved (PI. 43, fig.s 5 & 6). This surface is perforated by minute 

 rounded, hexagonal openings arranged in oblique, transverse rows which 

 gives them a more or less quincunx order, the interstitial spaces between 

 the openings are narrow, rounded ridges. There is no trace of a corneal 

 covering, and the surface is so much like that of the outer surface of the 



1 The Visual Organs of the Trilobites, Vet. Akad. Handl. 1901, 



