INTRODUCTION. 
Since the publication of the Monograph of North 
American Trilobites in 1831, the author has received 
from gentlemen devoted to natural science and fond 
of geological researches, a number of additional spe- 
cies belonging to this interesting group of fossils. 
Several of these have been described in the scientific 
~ periodicals of the day, and they are now collected to- 
gether in this supplement, for the convenience of 
those possessing the Monograph, and for the use of 
the artist who has so beautifully and accurately mo- 
delled the species described in our first essay. It is 
but an act of justice to copy from Professor Silliman’s 
Journal of Science and Arts, his estimation of these 
faithful imitations of nature; he observes, ‘* The 
Monograph is admirably illustrated by colored mo- 
dels done in plaster, by Joseph Brano, whose success 
in this effort must give full confidence that his talents 
can be advantageously employed on other occasions 
in the service of natural history. We are happy to 
see this application of the art of modelling thus fa- 
-vorably introduced into this country, it must be of 
great utility to cabinets and teachers, as well as to 
original investigators. We should be glad to see a 
complete set of models of all the known trilobites ; 
