igi I. No. 7. A NEW DOWNTONIAN FAUNA OF THE KRISTIANIA AREA. I7 



extending in broad flexible flaps, that are almost completelv coalescent 

 with the body on the inner side. The transverse plates on the sides 

 of the body are similar to those seen in Cephalaspis Miuchisoni Eg., 

 to which in its appearance this species has some resemblance. The 

 coalescence of the transverse plates with smaller ones is still evident. 



The fringe-plates are very short. The caudal fin is markedly heter- 

 ocercal. The underside of both the head and the body are covered 

 with very fine plates or scales. 



Very common in the fish horizon (III). In addition to a number of 

 fragments I found a quantity of more or less complete specimens in an 

 excellent state of preservation. 



Micraspis gracilis nov. gen. et sp. 



A small, slender form ; complete specimens exhibit a total length of 

 8 — 9 cm., of which the dorsal shield includes less than one-third. 



The dorsal shield, as in the previous instance, is furnished with 

 complete armour ; it is short and without dorsal spine. The corners 

 are truncated without horns. The\" here develop into comparatively 

 small, quite isolated flaps as in all the t\pical Cepludaspidae. 



The side plates are strong, almost upright; the fringe-plates long 

 and powerful. The caudal fin is ver\' long, and heterocercal. The under 

 side of the head is covered with somewhat large, irregular polygonous 

 plates; the under side of the body has strong transverse plates at the 

 sides, whilst in the middle we find \e\\ fine plates or scales in oblique 

 angular rows. 



This form approaches the real Cephalaspids in its construction. It 

 has been found in ver}' good specimens, although it is rarer than 

 Aceraspis. 



Anaspida Traquair. 



As regards the elegantly shaped Anasjnda, which occupies quite an 

 isolated position amongst Ostracoderms, three difl"erent forms occur in 

 the rich fish horizon (III). One of these is very common, whereas the 

 other two are comparatively rare. 



All exhibit a distinct relationship to the genus Birkenia Traquair. 

 The general shape of the body, the development of the dermal plates 

 or scales, the ventral row of strong projecting scales, and the remark- 

 able oblique row of small gill-openings Ç) agree throughout.. At the 

 same time they all difi'er in important features from the former, which 

 is the most typical, and the best known of Anasjiida. 



Vid.-Selsk. Skrifter. I. M.-x\. Kl. 1911. \o. 7. 2 



