THE LOWER DEVONIAN FISHES OF OEMUNDEN. 



729 



fig. 2 another detached example of this plate, a right one, is represented, also seen from 

 the sculptured surface. 



Closely within the outer narrow margin of this element x. is a small round opening 

 which perforates the plate through and through, from the outer to the inner surface. 

 Now, when we get a view of the inner surface as shown in PI. I. fig. 3, we perceive that on 

 this aspect of the plate the aforesaid opening is surrounded by a prominent thickened 

 ring-like margin. Here we have the explanation of the rounded pit seen in a 

 corresponding situation on the dorsal aspect of the carapace. It results, as is proved 



Fig. 3. — Restored outline of the ventral aspect of Drepanaspis Gemundenensis, Schl. Surface ornament omitted 

 and the tail twisted round so as to appear in profile. Lettering as in Fig. 2, but the mouth in front and 

 the cloacal opening behind are represented in black. 



by specimens worked out from both sides, from the dorsal armature above being 

 squeezed down on this ring, which therefore shoivs through, and produces the appear- 

 ance of a shallow pit with elevated edges as seen on the left side in PI. II. Why, in 

 this specimen, is no pit seen on the right side ? Clearly because the plate x. is on this 

 side removed from its place-— it is seen turned upside down, lying apart from, though 

 close to, the edge of the carapace — and consequently the ring-like margin of its per- 

 foration could not operate, as above indicated, in producing the shallow pit in question. 

 As to the function of this perforation, it is to be noted that it and the plate which 

 bears it occupy a quite similar position to the ocular plate and the supposed orbit o 



