61 



In the above list, I have left all the species in the genera to which they 

 were originally referred by their authors respectively. Some alterations 

 have been proposed by Prof. Hall and Dr. Shumard, which will no doubt 

 be adopted either wholly or in part. Without objecting to any of these 

 changes, it seems the better course, for the present, to admit D. D. Owen's 

 four genera, until more perfect specimens can be procured. 



On a comparative examination of all the genera in the above list it will 

 be seen, that Agnostns, Ulcemirus and Pempliigaspis are peculiar types, 

 and, in their organization, stand apart, as it were, from all the others. 

 Amphion is a well defined genus, now, for the first time, found in rocks 

 so ancient as the Potsdam, although it occurs in the Calciferous, and is 

 known in Bohemia, by a single species (J.. Lindauri, Barr.) in the lowest 

 beds characterized by the second fauna. These four genera are repre- 

 sented, so far as at present known, in the Potsdam by only seven species, 

 and constitute but a small portion of the whole fauna of the period. We 

 may also set aside Protichnites and Olimactichiites, becavise they consist 

 only of tracks, and we know too little about them to form any idea of 

 the affinities of the family to which they belong. 



After making the deductions, above mentioned, there remain thirteen 

 genera, and these all belong to one great family, which appears to have 

 attained its greatest development in the Potsdam period, and to have 

 gradually dechned afterwards, until the era of the Trenton limestone, when 

 it became extinct. The difierent generic groups, of which this family is 

 composed, are most closely allied, and run into each other in such a man- 

 ner as to render subdivision almost impossible, showing that they all had 

 one common origin. There appear to be, furthermore, innumerable varie- 

 tal passages between the species, while, in certain localities, the individuals 

 occur in such vast multitudes, although always in fragments, as to consti- 

 tute of themselves the principal mass of the rock. The aspect of 

 the family is that of a portion of the first fauna of Barrande, and it seems 

 probable that it existed in a period somewhat later than that of the large 

 species of Paradoxides, which form so striking a feature in the Primordial 

 zone of Europe. In Bohemia, Sweden, Wales and Spain, some of the 

 genera do indeed occur in the rocks of that ancient horizon, but they do 

 not constitute the principal and dominant section of the fauna. In the 

 Potsdam, on the other hand, thirteen out of seventeen genera (excluding 

 the genera founded on tracks), and fifty-three out of sixty species, belong 

 to this family, while the individuals are so exceedingly numerous that they 

 perhaps furnish ninety per cent, of the whole. 



Without noticing the Calciferous formation, for the present, we may 

 proceed next to the examination of the fauna of the Quebec group. In 

 the table shewing the succession of Canadian rocks, on page 20 of the 



