64 



Passing now to the upper part of the Lower Silurian we may, for our 

 present purpose, regard the Chazy formation as being characterized by a 

 distinct fauna ; but the Black River, Birdseye, Trenton, Utica Slate, and 

 Hudson River, should all be grouped together. The fauna of this latter 

 series may be called the Trenton fauna, as it attains its greatest develop- 

 ment in that formation. 



In the Chazy fauna the dominant family of the Potsdam trilobites is 

 reduced to a single genus and species Bathyurus Angelini. The genus 

 Amphion also passes from the Potsdam to the Chazy, but is not known 

 above that formation in this country. 



In the Trenton fauna the dominant family of the Potsdam is repre- 

 sented by only two genera (^Bathyurus and Triarthrus) . The latter has 

 not been found below the Trenton ; but it, nevertheless, is a genus of the 

 primordial type. Barrande has placed it in his third family, which includes 

 Paradoxides, Arionellm, Conocephalites, Olenus, &c. (Systeme Sil- 

 urien, p. 340.) In Canada we have four species of this genus, all in the 

 Utica slate, T. Beckii, T. spinosus, T. glaber and T. Canadensis. The 

 first of these is found, in New York, in the Trenton as well as in the 

 Utica slate. Of the three species of Bathyurus, two {B. Smithi and B. 

 extans) occur in the Black River limestone ; while the third (j. spiniger) 

 is common to the Black River and Trenton. 



In order to save space the generic relations of the several trilobitic 

 faunae above noticed may be abbreviated as in the following lists. 



TRENTON FAUNA. 



Asaphus, 10 ; Acidaspis, 2 ; Bathyurus, 3; Bronteus, 1 ; Calymene, 

 3 ; Cheirurus, 3 ; Dalmanites, 3 ; Encrinurus, 1 ; Harpes, 3 ; Illsenus, 7 ; 

 Lichas, 1 ; Proetus, 1 ; Triarthrus , 4 ; Trinucleus, 1. Total, 43. 



CHAZY FAUNA. 



Asaphus, 2 ; Amphion,! I ? Ampyx, 1 ; Bathyurus, I ; Cheirurus, 

 3 ; Harpes, 1 ; Illsenus, 6 ; Lichas, 1 ; Remopleurides, 1 ; Sphserexochus, 

 1. Total, 18. 



LEVIS FAUNA. 



Agnostus,3; Amphion, 5; Ampyx,!; Arionellus, 2; Asaphus, 

 4; Bathyurus, 12; Bathyurellm, 6; Cheirurus, 8 ; Gonocephal- 

 ites, I ; Dikelocephalus, 1 4 ; Endymionia, 1; Holometopus, 1 ; Har- 

 pes, 1 ; Harpides, 1; Illgenus, 5; Menocephalus* 3 ; Nileus, 1; 

 Lichas, 1 ; Remopleurides, 1 ; Shumardia, 1 ; Loganellus, 1 ; Cre- 

 picephalus; Ptychaspis; Bathynotus. Total, 73. 



