Dr Traquair on the Genus Gyracanthus {Agassiz). 97 



a want of lateral symmetry. M'Coy gives an outline of the 

 transverse section of G. oUiquus from a position considerably 

 proximal to the point, in which the two sides with the posterior 

 area seem as symmetrical as in Ctcnacantlins. In such a 

 spine it would be well to examine the extreme point. There 

 is in the collection of the Geological Survey of Scotland a 

 rather young spine from the Liddesdale beds, which I am 

 inclined to refer to G. dbliquus, and in it near the tip, the 

 transverse section has a form much resembling in general 

 characters that in M'Coy's figure ; but one margin of the 

 groove is nevertheless a little more prominent than the other. 

 It is to be hoped that American palaeichthyologists will care- 

 fully examine the spines of Gyracanthus occurring in their 

 country with special reference to the present question. 



2. The supposed Carpal Bones q/ Gyracanthus. 



Of constant occurrence in the same beds with Gyracanthus- 

 spines, and often found closely associated with them on the 

 same slabs of stone, are certain peculiar bones, first noticed by 

 Messrs Hancock and Atthey, and by them interpreted as 

 "carpal" bones. These occur of two forms or shapes, the 

 first of which was described by the above-named authors in 

 1868.^ It is a flat triangular bone, with a thick apex oppo- 

 site to a thin base ; and two other sides, one of which, the 

 longer, is slightly convex, the other, or shorter, being 

 straight or slightly concave : of the two surfaces one is 

 slightly convex, the other slightly concave in general contour. 

 Of these Messrs Hancock and Atthey say, '' Their structure 

 is very open ; and as they are seldom well preserved, they 

 are probably only imperfectly ossified; the bony fibre radiates 

 from the apex to the expanded base. There can be little 

 doubt that these are carpal bones similar to those in con- 

 nexion with the pectoral fins in sharks and dog-fishes." 



The second form is briefly noticed by the same authors in 

 another communication published four years later, and its 

 form is described as follows : — "This second form is probably 

 the inner carpal; it is a broad flat bone irregularly bilobed or 



1 Ann. & Mag. Nat. Hist, ser. 4, 1868, vol. "i,, p. 369. 

 VOL. VIII. G 



