FOSSIL FISHES. 17 



and salamanders have branched. In this original stock the characters of 

 all the derived groups are to be found, though in an imperfectly developed 

 state. Our modern fishes, for the most part, belong to the group called 

 osseous fishes, because they have complete bony skeletons, but in the 

 ancient fishes the quantity of dense bony tissue which formed their exo- 

 skeletons exceeded many times the quantity of bone in the modern fishes, 

 and it was apparently in structure more like the bones of amphibians and 

 reptiles than like the bone-tissue of fishes. Joined to this extreme devel- 

 opment of external bone was the cartilaginous vertebral column, which 

 was a mark of embryonic and rudimentary development. It is evident, 

 therefore, that the quantity and the perfection of bone tissue is no safe 

 guide in the classification of fishes. Tlie massive bones of Dinichthys 

 are very impressive, not only from their magnitude, but from their den- 

 sity and perfect preservation. None of the bones of reptiles or inammals 

 would have been, under the circumstances, more completely unaiiected 

 by the influences that have surrounded them. In this respect they are 

 evidently superior to the soft and elastic bony tissue which forms the 

 skeletons of most, and the highest, .modern fishes. We are compelled, 

 however, to regard the complete and impenetrable armor, and the massive 

 and formidable jaws of the great Flacoderms, as heavy and rude first 

 inodels, rather than the light, elegant, and efficient machines which are 

 the perfected results of a long process of improvement. The heavy armor 

 worn by the knights of old has long since been laid aside, for the mail- 

 clad warriors of the middle ages would be clumsy and powerless antago- 

 nists to our light-armed troops, carrying repeating rifles and revolvers, 

 and moving with the celerity and precision of modern tactics. So in the 

 progress of ichthyic life, increased intelligence, rapidity of movement 

 and address, have proved in the struggle of life more than a match for- 

 the impenetrable but cumbrous defenses of the sluggish and over-loaded 

 Placoderms. 



Facts of like import may be found in the life-history of all classes of 

 animals, and those not less real and suggestive in the history of man and: 

 the progress of civilization. 



In a note appended to a preceding page, I have called attention to- 

 another point in the structure of Dinichthys which may possibly show a 

 relationship between the Placoderms and the Teleost fishes, and it may 

 even be with the higher classes of Vertebrates. This subject is one of 

 such interest that I venture to again call attention to it. By reference to 

 the figures now given of the ventro-pectoral shield of Dinichthys,. it will . 

 be seen to be composed of two pairs of flattened bones, which apparently 

 held some relations with the pectoral and abdominal fins. This is clearly- 

 shown with regard to the posterior pair by the deeply excavated' furrows ■ 

 2 ' 



