l8 • JOHAN KIÆR. M.-N. Kl. 



The most striking difference is found in the arrangement of the 

 narrow dermal plates on the sides of the body. 



In the case of JHrkenia, these are chiefly set in regular oblique 

 rows inclined forwards and downwards. In the new Norwegian forms 

 they very distinctly separate into a dorsal and ventral section on both 

 sides of a median line: above this they incline forwards, below this back- 

 wards. Thus they meet along the whole median line in regular angles, 

 a peculiar feathery arrangement of the median dermal plates, giving 

 these forms a characteristic appearance cjuite distinct from Dirkenia. In 

 consequence of this characteristic I have chosen the name Pterolepis 

 for the most common of the new forms. There are, however, other 

 differences that need not be mentioned here. The Norwegian forms 

 must in consequence be placed in a new family Pterolepidae, adjacent 

 to Birkenidac, Lasmriidae and Euphaneroindae. 



In this new family it seems apparent, that the dermal plates at the 

 side of the body correspond to the myotomes. 



In the most primitive of the new forms, Pterolepis nitidus, nov. 

 gen. et sp,, the head is covered with small scales, about the same as in 

 Birkenia. In another much larger form a peculiar system of large der- 

 mal plates has been developed on the under side of the head, while the 

 other part of the head is covered with fine scales. I have therefore 

 named this form Phärgngolepis oUongus nov, gen. et sp. In a third 

 one, which is quite small, and which has been named Rhijncholepis 

 parvulus nov. gen. et sp., the upper part of the head and the snout are 

 also covered with a peculiar series of large dermal plates reminding one 

 of the cranial bones of the Crossopterygii. 



In this preliminary report I cannot give a more detailed account 

 of these extremely interesting differentiations, which indicate remarkable 

 new stages of development from the primitive forms which have hitherto 

 been known as Anaspida. 



Pterolepis nitidus nov, gen. et sp. 



The dimensions of this form are about the same as in Birkenia 

 elegayis Traqu. In specimens of medium size the total length is thus 

 about lo cm., but both smaller and considerably larger examples occur. 



Ecxluding the different arrangement of the dermal plates on the 

 side of the body, this form does not differ very widely in the other 

 characteristics of the exoskeleton from Birkenia. The dorsal fin, how- 

 ever, is quite differently constructed, for the front is provided with a 



