58 MONOGRAPH OF DURA DEN. 



the species, as well as intlividuals of this type of fishes. They are extremely 

 ornamental, regularly and beautifully arranged, and cannot fail to fill with 

 admiration the most indifferent observer. Their glossiness of colour, roundness 

 of form, firmness of texture, deep-set groovings of tracery, and comparative 

 largeness of size, at once mark the family as one of peculiar interest, a sin- 

 gular combination of strength and harmony in animal structure. They have 

 been represented as " the scavengers" of the seas in ancient geologic times; 

 we would rather say they were the "rover-kings" who issued from their 

 rocky fastnesses, armed cap-a-pie in cuirass and mail, and able to do battle 

 with every ocean tribe that opposed them. 



The scales, according to M. Agassiz, consisted of a dense, thick osseous 

 substance, formed in parallel and superposed beds, and turned against the 

 inner edge of the skin, while concentrated markings of growth, repeating 

 the figures of the scales, are distinctly traceable over all the surface. They 

 are crossed by fine rays, radiating from the centre outwards, which are formed 

 by very delicate channels scarcely in relief, and in which were probably fixed 

 the fibres of the skin. Numerous small canals, conductors of the blood- 

 vessels, ascend by these rays into the substance of the scales, and near the 

 surface they branch out horizontally, forming a very straight net-work of 

 mail. Above this net-work — indicating the space between the osseous and 

 enamelled substances — lies the enamelled bed which occasions the external 

 ornament and fine-tint material of the organ, and the bed itself is only a 

 thicker osseous membrane through which the corpuscules are ramified and 

 diffused. 



The form of the scales is uniformly, in all the Old Red species at least, 

 oval or rounded, and many of them on particular parts of the body, are nearly 

 circular. This is remarkably the case with all on the ventral side, which by 

 compression, I observe, in a great many instances, are detached or in slightly 

 connected rows, and the circular tendency is clearly manifested. The scales 

 are imbricated, or slightly raised — the one edge of the superior, along the 

 median line, and from the head lengthways, over the posterior in their suc- 

 cessive courses. The covered part is smooth and devoid of ornaments, whilst 

 the exposed part of the surface is richly ornamented by longitudinal ridges 

 and eminences, radiating, or more and less diffused, extending to the extre- 

 mities, or leaving an outer border and even selvedge across the edge of the 

 scale. The arrangement of these ridges and groovings serve not only to distin- 

 guish the different species, but to determine the character and to give name to 

 the genus — Holoptychius — the holos and ptyclie — the entire wrinkled scale fish. 



The mode of formation of this organ in fishes resembles the growth of hair, 

 feathers, and wool in other animals, and consists of nearly the same elements 

 as hoofs, beaks, claws, and nails. An extremely delicate and finely organized 

 pulp, composed partly of a congeries of minute vessels, and partly of a gela- 

 tinous substance in which these vessels are imbedded, constitutes the appa- 

 ratus by which the nutrient particles are selected, combined and elaborated 

 into the materials of the intended structure. Tlie original form, situation, 

 disposition, and mass of this vascular pulp, determine the future figure and 

 extent of the growth of the organ on the several kinds of fishes to which they 



