19 
tail of this highly interesting fossil, comprised all of 
the animal which has yet been found. Eleven ar- 
ticulations of the middle lobe, and ten of the lateral 
lobes are quite distinct. - All the costal arches or 
ribs are smooth and rounded, being without pustula- 
tions, strize or grooves. Four of the upper arches of 
the dorsal, or middle lobe, are longer than those on 
the sides of the body, a peculiarity which i 
ciently decisive to mark. the species. Indeed 
organization furnishes a striking exception to the 
generic characters of the Asaphus, as: given by Pro- 
fessor Brongniart, who states ‘‘ that the middle lobe 
of the abdomen: 1 is rarely more than one-fifth the width 
he body.” But what is more remarkable, and 
r di stinguishes this animal remain from all 
phs, is the epidermal covering which con- 
led the terminal articulations of the tail. In our 
specimen there is no appearance of what has been 
called the membraneous development beyond: the 
lobes of the animal, another circumstance which 
seems to separate it from the genus Asaphus. ‘The 
body is quite convex, and both in breadth and length 
our fragment measures nearly three inches. 
I am indebted to the kindness of Dr. Charles T. 
Jackson, of Boston, Massachusetts, for this species; 
it occurs in magnetic iron ore, and was found by Dr. 
Jackson and Mr. F. Alger, during their geological 
tour through Nova Scotia. Their highly important 
memoir describing the mineralogy and geology of 
