384 



FOSSILS.. 



Of the other genera, we know Asaphus, Illasnus and Ceraurus (=Chierurus) in the Trenton limestone 

 and Hudson Kiver groups ; Illasnns and Ceraurus in the upper Silurian strata of Niagara age, or the 

 third fauna of Barrande; while Ceraurus occurs also in the Devonian of Europe. Amphion is known in 

 the second fauna in Europe, and, doubtfully in the first. 



Ceraurus does not occur in this country, so far as I know, above the Niagara group; though known in 

 the Devonian rocks of Europe. 



The following tabular arrangement of the genera found in the Quebec group will serve to express more 

 distinctly the relations of the Crustacean fauna of these rocks. 



The letters at the head of the columns have the same references as those used in the communication of 

 Sir William Logan. 



In this table we find, of previously recognized trilobites of the primordial fauna, two genera and five 

 species; of previously known genera of the second and third faunae, four genera and eight species; two 

 genera before known in the Potsdam sandstone and seven species; and of Agnostus, which is of the first 

 and second faunse, two species; and one new genus with nine species. 



These are certainly very curious results; and a modification of our views is still required to allow four 

 genera and eight species, (or leaving out Amphion) three genera and six species of the trilobites of the 

 second fauna, to be associated with two genera and five species of trilobites of the primordial fauna, and 

 yet regard the rocks as of primordial origin. 



The Brachiopodous genera, Lingula, Discina, Orthis, Lepteena and Strophomena, have a great vertical 

 range, and are known in the lower and upper Silurian, and most of them in the Devonian; while Camarella 

 so far as known is a lower Silurian form of the second fauna (perhaps also in a lower position.) 



Of the Gasteropoda, Maclurea and Ophileta are restricted to lower Silurian rocks, but occur mainly in 

 the second fauna. The other genera occur likewise in the second fauna and in the upper Silurian rocks, as 

 well as some of them in Devonian. The same is true of the Cephalopoda enumerated. 



Tetradium is known in the second fauna of the .lower Silurian rocks, and in the upper part of the 

 Hudson Eivcr group at the west. Dictyonema is a genus known from lower Silurian to Devonian strata. 



Grraptolithus proper extends to the Clinton group of New York; and the same is true of Reteograptus. 

 Thamnograptus occurs in the rocks of the Hudson River group near Albany, and in the Quebec rocks. 

 Phyllograptus and Retiolites arc known in the Quebec rocks only; while the typical form of Dendrograptus 

 occurs in the Potsdam sandstone, and, likewise, in three other species, in the Quebec rocks. 



We find, therefore, in the other genera except trilobites, very little satisfactory evidence, on which to 

 rely in the present state of our knowledge, for determining the position of these strata. 



