86 



GENUS TRIARTHRUS. Green. 



Body, slightly convex; contractile? 



Buckler? 



Abdomen, with three articulations, side lobes longi- 

 tudinal, narrow, and wedge-shaped. 



Tail, broad, rounded, without any membranaceous 

 expansion. 



The name of this genus is derived from the cir- 

 cumstance, that the abdomen has but three articula- 

 tions; an organization which is very peculiar. These 

 curious fossil animals are very abundant in the rocks 

 in which they are found; but though I have examined 

 a multitude of specimens from different localities, no 

 vestige of the head or buckler could, on the most mi- 

 nute examination, be discovered. Whether these ani- 

 mals, during their petrifaction, were so contorted or 

 rolled up, as to bring the extremities of the body to- 

 gether, in such a manner as to present the posterior 

 folded part only to the view; or whether the buckler 

 has been destroyed by the process of mineralization, 

 as appears frequently to happen with the asaphs, we 

 are at a loss to determine. 



The animal remains which belong to the genus 

 Triarthrus, differ so much in their' form and general 

 characters from all the other trilobites,thatwe perhaps 

 ought to regard them as forming another race of be- 

 ings. They are, however, more nearly allied to this 

 family than the Agnosti of Professor Brongniart. 



