EXPLANATION OF PLATE 2 C 



1 DIPLOPTEEAX GRACILIS (M-'Coy). Natural size ; from the black Devonian flags of Orkney. 

 J a Scale of ditto, magnified 2 diameters, shewing the punctm-ed external polished surface. 



1 b Internal surface of scale of ditto, shewing the articular ridge. 



■I GYROPTYCHIUS ANGUSTUS (M<^Coy). Natural size; from the Devonian flags of Orkney. 



2 a One scale from back of another specimen, magnified 3 diameters. 



3 GYROPTYCHIUS DIPLOPTEROIDES (M'^Coy). Natural size; from the bituminous Devonian 



flags of Orkney; (with a lens of low power, the gyrate sculpturing of the scales may be seen). 



3 a Two lateral scales of ditto, shewing the gyrate sculpturing of the surface and the two articular 



margins, magnified 3 diameters. 



4 COCCOSTEUS MICROSPONDYLUS (M^Coy). Natural size; from the black Devonian flags of 



Orkney. On the lower left-hand portion of the dorsal plate, at upper part of figure, is seen appar 

 rently the remains of a spine attached thereto ; the left-hand extremity of the figure shews the 

 remains of the vertebral column, ehibiting the separately ossified bodies of the vertebrae with several 

 neurapophyses, and a few distinct traces of the lower spinous processes or hsemapophyses, and below 

 them the dermal bones of the dorsal fin in reversed position. 



5 COCCOSTEUS PUSILLUS (M-'Coy). Natural size of full grown specimen ; from the Devonian 



flags of Orkney. The lower part of the figure shews two united posterior latero- ventral plates, under 

 and immediately above which is seen the extremity of the dorsal plate ; the remains of the vertebral 

 column seem only to have the spinous processes ossified, the right-hand or anterior end of the figure 

 (which shews the ventral aspect) exposes the two dislocated halves of the lower jaw with their teeth. 



5 a Single perfect dorsal plate of ditto, from another specimen, natural size. 



6 COCCOSTEUS ?TRIGONASPIS (M^Coy). Probably mesial ventral plate, natural size. 



6 a Tuberculation of ditto, magnified. 



7 CONCHODUS OSTRETFORMIS (M^Coy). Palatal tooth, natural size; from the Old Red con- 



glomerate of Scat craig. 



