: , : * ° A 
38 
one of the cheeks, and a portion of the front are ob- 
scured by the rock in which the animal is imbedded. 
The cheeks form spherical triangles. The oculife- 
rous tubercles, though a good deal defaced, seem to 
have been circular and not lunate, as in the A. Cau- 
datus. A raised, curved line passes from and over the 
eye, between it and the lateral lohgen of the abdomen. 
The, central lobe of the back is $composed of twelve 
double joints, and that of the tail of six single articula-_ 
tions; where the epidermis or shell is perfect, all the 
articulations appear single. The last joint of the tail 
is longer than in any other of our species. The ribs 
of the abdomen are rather broad, and have a deep 
furrow scooped out along their upper surfaces their 
extremities, where they can be discovered, are de- 
tached from each other, and terminate in reflected 
points, like those of the A. Limulurus. The costal 
arches of the tail are delicately grooved and termi- 
nate in the membrane. The membranaceous eXpan- 
sion round the edge of the tail is very narrow, and 
appears to form no projection beyond its central 
part. The whole epidermis is. finely marked with 
granulations. Length one inch and three-fourths— 
breadth one inch and one-fourth. : 
This interesting species was found in jnetine 
shale, near Rochester, in Munroe County, N. Y.; and 
is now in the valuable cabinet of the Albany Institute. 
An accidental fissure of the rock disclosed not only a a 
fine specimen of both the mould and the cast of this 
animal, but also another individual of the same sp 
cies in contact with it, From the peculiar attitud 
