Devonian Fish- Fauna of Spit zhergen. 7 



Plates of tvniik ornamented witli numerous fine tubercles, of 

 which the majority are arranged in concentric series. 



A second species of Acanthaspis from the Lower Devonian 

 of Spitzbergen is indicated by the small slab of remains, 

 partly shown in PI. II. figs. 2-5. In addition to several 

 portions of the characteristically ornamented plates, the fossil 

 exhibits parts of two or perhaps three lateral appendages. 

 There are also two other plates exposed from the inner aspect, 

 the one having the appearance of the occipital region of the 

 cranial shield, while the other is irregularly quadrate and not 

 readily determinable. 



The best-preserved fragment of a lateral appendage is 

 enlarged twice in PI, II. fig. 3, and displays portions of the 

 sparsely nodose, rounded, longitudinal ridges, with some of 

 the stout, backwardly pointing tubercles on the inner or con- 

 cave border. Another fragment shows that the plate (either 

 dorsal or ventral) at the base of the appendage is tuberculated 

 like the remainder of the armour and exhibits no arrangement 

 of ridges. 



The supposed occipital plate (PI. II. fig. 2) is thus deter- 

 mined because it is bounded on one side by an attenuated 

 border gently excavated in a symmetrical manner with respect 

 to a short broad process (;>), which is very suggestive of the 

 median process of the occipital shield in the Asterolepidas. If 

 the element pertains to the same individual as either of the 

 appendages, it is remarkably large; but it may be equivalent to 

 the median occipital and lateral occipitals of the Asterolepidse 

 fused together, and the plates in the fossil under discussion 

 may represent several individuals. 



The small quadrate plate, which is shown of twice the 

 natural size in PI. II. fig. 5, is worthy of note as being 

 unbroken except at the border directed inferiorly in the 

 drawing. Near the upper end of one of the borders placed 

 veitically there occurs a short truncated process ; and at the 

 same extremity of the plate there is a broad triangular 

 depression on the exposed inner face, evidently to be inter- 

 preted as a surface of overlap. A vertically elongated mesial 

 excavation also extends from the edge of this facette down- 

 wards. 



Form and Loc. Eed Micaceous Sandstone, Dickson Bay. 



