Mr. R. Walker on Fossil Fishes of Dura Den. 75 



to the free edges, and seldom anastomose ; but along the belly 

 and towards the back, above the lateral line, where the sculp- 

 turing becomes bolder and sharply defined, anastomoses more 

 frequently take place between the lines or ridges. 



So far as yet stated, there is nothing to indicate more than 

 specific differences ; but when these scales are closely examined, 

 a number of small and very distinct points or tubercles are seen, 

 which form a semilunar or crescentic area on the posterior part 

 of the first half of each scale, and immediately in front of the 

 exposed sculpture. These tubercles appear as radiating in 

 straight lines from a centre, which is not itself apparent, and 

 are best seen on the scales that cover the sides of the fish. I 

 have found them, however, more or less distinctly indicated, on 

 well-preserved specimens, on nearly all parts of the body, from 

 the ventral to almost the extreme dorsal edge. When the scales 

 are entire, these crescentic areas are almost hidden by the over- 

 lapping of the anterior scales, and, excepting a very small part, 

 they may be said to be altogether concealed. When the scales 

 are not well preserved, of course these tubercles are obliterated 

 altogether; but when well-preserved specimens are met with, 

 and the overlapping scales are absent or removed, then these 

 tubercles are very distinct and easily recognized (fig. 2) ; and 



Fig. 1. Fig. 2. 



ill VIII III lm).li 



IIP 



Fig. 1 . Scale of Glyptolepis, from the side ; natural size. 

 Fig. 2. Scale of Holoptychius Flemingii, from the ventral surface, about 

 two inches behind the jugular plates ; natural size. 



when compared with specimens of undoubted Glyptolepis (for 

 which I am indebted to the kindness of Mr. Powrie), and then 

 with the figures and description of the scales of that genus in 

 Prof. Huxley's essay, ' Decade X./ the resemblance is at once 

 apparent and unmistakeable. In some cases the resemblance is 

 even closer to the figure from Pander, given in the above decade, 

 than to that of the figures by Huxley, which were drawn (as he 

 says) from a scale of Glyptolepis from Wick. To Prof. Pander- 

 is due the credit of having first discovered the true sculpture of 

 the scales of Glyptolepis, which he wrought out of a Lethan-Bur 

 nodule ; while Prof. Huxley has still further elucidated and con- 

 firmed the matter, which he says he did by " scraping away the 

 inner layers of the scales of undoubted examples of this genus 



6* 



