from the Scotch Old Red Sandstone. 309 



hind the head, where it is one-seventh of the length, tapering 

 very gradually from thence to the tail, the pedicle of which is 

 about one-third the greatest depth of the body; caudal fin 

 large, rhomboidal, obtusely pointed behind, lower side largest, 

 the supramedial spinal prolongation extending nearly to the 

 end ; posterior anal fin semi-elliptical, equalling the depth of 

 the body at its base in height, which is about double the 

 length ; both the posterior anal and dorsal fins nearly touch 

 the caudal, and are fully their own height behind the anterior 

 and dorsal fins, which are about one-third less in size ; the 

 pectoral fins are broad ovate, scarcely two-thirds the depth of 

 the body at their base in height, and placed nearly their own 

 height behind the head ; scales about 2 lines high (or wide) 

 and about one-third longer, elliptical and with a small, nearly 

 central boss, round which seem to gyrate very numerous mi- 

 nute rough ridges, less than their own diameter apart, which 

 are arranged in converging curved lines parallel with the mar- 

 gin of the elliptical free end of the scale ; the small portion of 

 the ridges anterior to the central boss are frequently broken 

 into little tubercles ; the more anterior concealed portion is 

 smooth or very minutely radiated, the (? articular) ridge on 

 the under side strongly marked ; bones of the head closely 

 sculptured with small granules and short vermicular ridges. 

 Length nearly 1 foot; length of exposed portion of scales 

 slightly more than 2 lines. 

 This beautiful fossil much resembles the Diplopterus gracilis 



(M'Coy) in form, but is at once distinguished by the structure 



and sculpturing of the scales. 



Rare in the old red sandstone of Orkney. 



(Col. University of Cambridge — two fine examples.) 



Gyroptychius Diplopteroides (M'Coy). 

 Sp. Char. Head semi-elliptical, depressed, sides flattened, slightly 

 longer than wide, pointed in front, about one-fifth of the entire 

 length ; body tapering rapidly from the head to the tail, the 

 pedicle of which is less than half the width of the body ; cau- 

 dal fin rather large, rhomboidal, submedial spinal prolonga- 

 tion slender ; posterior dorsal elliptical, twice as high as long, 

 close to the base of the caudal, and reaching about half the 

 length of its lateral angle ; anterior dorsal little more than 

 half the size of the posterior ; pectorals short, broadly rounded, 

 placed rather more than their own length behind the head ; 

 scales of the back oval, imbricated ; concealed portion, anterior 

 to the subcentral point, smooth or very minutely radiato-punc- 

 tate, all the posterior or exposed portion rough with small, 

 irregular, minutely flexuous ridges, those of each side running 



