DESCRIPTION OF THE FOSSIL REMAINS. 61 



small, and placed high up on the sides of the body, the thoracic girdle rather 

 feeble, and there seems to have been but slight development of these fins." 



Had the whole recent discoveries of Dura Den been lying on the cabinet- 

 tables of the eminent naturalist, he could not have furnished, from a com- 

 parison of the mass of specimens before him, anything more descriptive and 

 accurate than what is here related. From an examination of hundreds of the 

 most clearly-defined fossil remains, of all sizes of bodies, from six inches to 

 forty, we have been able to verify every one of the details in the picture. 

 The vast depth and breadth over the shoulders of the large specimen recently 

 dug up in Dura Den, show how well Nature has attended to the laws of 

 gravity and equipoise in placing, as she there has done, the pectorals " high 

 up on the sides of the body ;" while Agassiz' own profound knowledge of 

 structural conditions is verified to the letter in the " considerable de-C^elopment 

 of that locomotive appendage," the caudal fin, or, rather I should say, the 

 system of fins. The specimen of this organ now in Lord Kinnaird's collec- 

 tion measures exactly nine inches in length from the termination of the 

 scales to the extremity of the fin-rays in the tail ; it is five inches and a half 

 in breadth, and consists of three distinct groups or cords of rays, uniting at 

 the roots, but separable outwardly on their extended radius. The form of 

 this powerful propeller, on the terminal fulcrum of motion and strength, 

 is that of a graceful fan in repose, and shows its expansive capacity of 

 development, when unfolded, in the massive assemblage of filaments of which 

 it is constructed. 



Nor, let it be remarked, does this thick and condensed cordage of fin-sub- 

 stance conceal the normal structure of the caudal portion of the skeleton. The 

 normal arrangements are fully manifested, where in this largely developed 

 specimen the upper fin-lobe is comparatively smaller, and the extended verte- 

 bral column very distinctly defined. It is the same in one and all of the 

 innumerable specimens furnished in this prolific locality. And I simply 

 notice the fact, because in the last posthumous edition of the Old Red 

 Sajidstone of Hugh Miller, a figure of the Holoptychius, from Dura Den, is 

 there given with the homocercal representation of the fin -organ, and shorten- 

 ing of the vertebral column. The engraving, in every particular, is defec- 

 tive in execution ; and compared with the fossil specimen itself, it is equally 

 defective in the scales, and inaccurate in omitting the vertebral column, 

 which in the specimen is distinctly traceable to the extremity of the tail-fin. 



There are fourteen species of this genus known and described, of which six 

 belong to the Old Eed and eight to the coal measures. Their chief distinc- 

 tions consist in the form and granulation of the scales, and in the size and 

 position of the fins. Thus the scales of Iloloptychius Flemingii are very much 

 longer than broad on the sides, but round under the belly, and the ornaments 

 form undulating lines running horizontally towards the posterior edge, without 

 any visible ramification. The Holoptychins Andersonl is partly characterized 

 by the absence of the tubercular zone, by the extension of the folds to the 

 posterior edge, and by the length equalling nearly the breadth. The scales of 

 Holoptychius Murchisoni differ from both in the greater elevation of the 

 ridges, in their distinct and confluent ramification towards the posterior 



