GENERAL OBSERVATIONS. 395 



the abundance of the remains of fishes in the Devonian, makes their absence 

 from the American Silurian, and from all the foreign below the Upper Ludlow 

 beds, the more striking, and adds force to the conclusion that no fishes existed 

 during that era. And the same holds true with regard to the absence of Rep- 

 tiles from the Devonian age. On this ground alone, the supposed discovery by- 

 Pander of microscopic teeth of fishes, in the Russian U ngulite grit, of the Lower 

 Silurian, with no knowledge of fish-relics elsewhere in the Silurian of America 

 or Europe, would be reasonably questioned, were it not also proved that these 

 so-called teeth were not ichthyic, but probably from the dental apparatus of Gas- 

 teropods. 



It is an error, as the facts reviewed have shown, to suppose that 

 the system of life commenced with the lowest forms, and reached 

 always a higher grade with each new development. The following 

 are some of the principles bearing on this progress which have 

 been exemplified in Palaeozoic history. 

 (l.)The earlier species were water species, and all of them marine. 



Radiates and Mollusks the water Articulates, and Fishes the 

 water Vertebrates, comprise all known species of animals until 

 the close, or nearly the close, of the Devonian ; and Sea-weeds all 

 the plants to the close of the Silurian. In all divisions of the 

 kingdoms of life the species made for the water are of inferior 

 grade. 



(2.) Many of the earlier types were of the kind called comprehensive 

 types, as explained on pp. 203, 302. 



Trilobites and the Ganoid fishes have been mentioned as ex- 

 amples. Other examples are — the Labyrinthodont Reptiles, which 

 comprehended, along with the structure of the Amphibian, the 

 scaly covering and some other peculiarities of the higher Rep- 

 tiles ; the large Lcpidodendrids of the Coal era, which combined 

 with the characteristics of the Cryptogams the foliage and general 

 habit of the Conifers ; the Sigillarids, which presented the general 

 structure of the Conifers, with a habit and foliage that approxi- 

 mated them to Lepidodendrids ; the Catamites, which possessed 

 the habit of the Equiseta among Cryptogams, united, in some 

 species at least, according to Brongniart, to a woody texture ap- 

 proaching that of the Sigillarids ; and, in the early Silurian, the 

 Cystideans among Radiates, which often had a want of radiate 

 symmetry almost as great as characterizes Mollusks, and also some 

 features of the later Echinoids joined with the essential structure 

 of the Crinoids. 



These comprehensive types, as is apparent in the examples, do not 

 occupy a middle point between two of the general divisions of the 

 Animal kingdom : on the contrary, they belong fundamentally to 

 one, while partaking of some of the characteristics of the other. 



