EXPLANATION OF PLATE 2. B. 



1 CHIRACANTHUS GRANDISPINUS (M<^Coy). Natural size. At the point of greatest curvature 

 of the back the single dorsal fin, and its thick spine, are partially preserved. 



1 a Scales of do. from near the tail, magnified 24 diameters. 



2 CHIRACANTHUS PULVERULENTUS (M<^Coy). Natural size, small perfect individual, from the 



black Devonian flags of Orkney. 



2 a Scales of do. from about the middle of a somewhat larger specimen, magnified 24' diameters. 



3 DIPL ACANTHUS PERARMATUS (M<^Coy). Natural size, wanting the head, from the black 



Devonian flags of Orkney. 



S a Scales of do. from near the middle, magnified 24 diameters. 



4 DIPLACANTHUS GIBBUS (M-'Coy). Natural size ; wanting the head. (The small patch of scales 



does not clearly shew their mesial prominence). From the black Devonian flags of Orkney. 

 4 a Scales of do. from near the middle, magnified 24 diameters. 



