NEW SPECIES OF TRILOBITE. 221 



And if such is the approximation of opinion to unity, in this 

 more unsettled part of geology, equally cheering is it to look at 

 other departments of the science. Not many years since, the 

 main controversies related to the nature of the causes of geological 

 change. Now, by means of the labors and reasonings of able 

 men, and eminently of the distinguished gentleman* from the 

 land of our fathers, who has honored our country with a geolo- 

 gical visit, and this meeting by his presence, the ground of dispute 

 is narrowed down to a consideration of the intensity of causes in 

 whose nature all agree. It is possible that the question of uni- 

 formity and of catastrophes may never be completely settled : and 

 quite possible also, that a complete physical theory of geology 

 may never be attained, because beyond human sagacity. Yet 

 phenomenal and inductive geology is fast assuming a fixed and 

 symmetrical form in all its parts : and when this work is com- 

 pleted, inquuies into the origin of things, may lawfully form the 

 pastime of geologists. 



On a New Species of Trilobite of very large Size. By 

 John Locke, M. D., Prof, of Chemistry and Pharmacy in 

 the Medical College of Ohio. Read April 6, 1841. 



Isotelus Megistos. 



Clypeo antice elliptico, attenuate marg-inato, postice arcuato, et 

 terminato ntrinque aculeo ; cauda postice ellipticd, antice arcuatd ; 

 articulis abdominis octo. 



The shield is anteriorly neai-ly perfectly elliptical, broadly and 

 thinly margined, posteriorly arcuate, and terminated at the angles 

 by spines or pointed processes extending backwards beyond the 

 two first abdominal articulations. The eyes are prominent, large, 

 furnished exteriorly each with a crescent-shaped cornea, and 



* Charles Lyell, Esq. 



