ASTEROLEPIS MAXIMA. 89 



lozenge-shaped, with truncated proximal and distal angles ; the proximal extremity 

 taking part in the formation of the elbow- joint as already described, the lower 

 joining the terminal plate (t.). Above the lateral obtuse angles the plate articulates 

 with the upper external and internal marginals, and under it with the lower plates of 

 the same name. The upper marginal of each side is a plate sharply folded on 

 itself, taking part above in the elbow-joint by passing its smooth articular upper 

 extremity under the corresponding marginal of the upper arm ; it has a dorsal 

 and a ventral edge, which articulate with the respective dorsal and ventral cen- 

 trals, and a lower extremity which touches the lower marginal. Each lower mar- 

 ginal is conformed similarly to the marginals of the upper arm, being wide in the 

 middle, narrow above and below ; it is also sharply longitudinally folded on itself, 

 and articulates with the upper marginal proximally, the central mesially, and the 

 terminal mesially and distally. 



The terminal forms the sharp extremity of the limb, articulating proximally with 

 the dorsal and ventral centrals and the lower marginals. It is hollow internally, 

 the cavity of the limb being continued into it till very nearly to its apex. 



It is here to be remarked that the sharp inner edge of the forearm is often seen 

 to be prominently denticulated in the manner shown in PI. XVIII, fig. 7. This is 

 the appearance which led Agassiz to establish the genus Odontacanthus on a fragment 

 of a marginal plate from a forearm of Aster olepis. 



Tail. — No remains of any tail have ever been found, but that is not remarkable, 

 seeing that the remains occur in so disjointed a condition. I have seen one or two 

 small and badly preserved scales from the same beds, which might have belonged 

 to the tail of Asterolepis maxima, but of that no evidence can be adduced. 



In conclusion, I may remark that the specimens figured in Pis. XV, XVI, 

 XVII, and XVIII are all from the quarries at Kingsteps, near Nairn, and are con- 

 tained in my private collection. 



Postscript. — Since the preceding pages have been in type I have, after careful 

 consideration, come to the conclusion that Ghelonichthys, Agassiz, ought to be 

 removed from the list of synonyms of Asterolepis, Eichwald. For although 

 Agassiz records how he became convinced of their identity, and therefore withdrew 

 his generic name in favour of Eichwald's, this seems simply to have been a 

 mistake, as there is no proof that he ever applied the name Ghelonichthys to any 

 species of Asterolepis. The two species which he included under that name in his 

 " Tableau general" 1 were Oh, Asmussii and Oh. 'minor. Of these, the former 

 undoubtedly belongs to Asmuss's genus Heterosteus, while as to the latter, 

 whatever it may be, there is no evidence for its being assigned to Asterolepis. 



1 ' Poiss. Foss.,' vol. i, p. xxxiii. 



