191 I. No. 7. A NEW DOWNTONIAN FAUNA OF THE KRISTIANIA AREA. 19 



powerful fin spine leading into a basal plate, a condition which hitherto 

 has not been found in any Ostracoderm, but which reminds us of the 

 construction of the fin in Acanthoderms and the Selachi. Ventral scales 

 are much more numerous than in Birkenia; in this respect Pterolejns 

 more closely resembles Lnsaniiis. 



Very common in the fish horizon III; a large quantity of excellent 

 specimens have been discovered. 



Pharyngolepis oblongus nov. gen. et sp. 



This form is greatly elongated, almost eel shaped, and it is much 

 larger than the previous one. The total length is at least 20 cm. 



The exoskeleton entirely agrees in its main features with that of 

 the previous species. The dermal plates on the head, on the contrary 

 are quite different. The sides and upper portion of the side are covered 

 with small elliptical or somewhat pointed scales, whilst the under side is 

 provided with a system of larger plates of a very unique character, 

 having the appearance of being a coalescence of the small scales that 

 cover the under part of the head in Pfcrolcpis. 



The ventral scales are very numerous but not so sharp as in 

 Fterolepis and the dorsal fin in this case lacks the remarkable dorsal 

 spine. 



This interesting species is rare in the fish horizon III. In addition 

 to a number of fragments, only three somewhat complete specimens 

 have hitherto been found. 



Rhyncholepis parvulus nov. gen. et sp. 



This form is quite small, the total length seldom exceeding 7 cm. 

 The shape of the body is about the same as in Birkoria. 



The exoskeleton is almost the same as in Pterolepis. The covering 

 of the head with plates is however quite different both from the latter 

 and Pliaryngolepis, for the upper side is decked with a unique system 

 of plates which remind one somewhat of the cranial bones in the 

 Crossopterygii. The sides also, and the under side of the head arc 

 covered with dermal plates of considerable size. 



The dorsal fin has no fin spine, but in front there are two large 

 flat plates; the shape is somewhat flat, and much more elongated than 

 in the other forms. This tiny form, which appears to present the grea- 

 test dift"erentiation within the Pterolepidce, is also not very common in 

 the fish horizon III, 



It occurs in a number of good specimens. 



