49 
to give the. side of the animal a serrate appearance. 
The costal arches of the tail are grooved through 
their whole extent, and present no spinous termina- 
tions. Beyond the membranaceous expansion of the 
tail, which is somewhat similar to that of the Asa- 
_ phus Caudatus, there projects a single spine, like 
a i 
that from the tail of the Limulus polyphemus; this 
spine may be traced under the caudal membrane to its 
insertion into the middle lobe. A portion of the 
crustaceous shell is still entire, and it seems to have 
been covered with very minute granulations. A 
row of large granulations may easily be traced on 
each side of the middle lobe. Length of the frag- 
ment, one inch and a half. Breadth one inch and a 
fourth. 
The A. Limulurus was found in the dark brown, 
shaly limestone, at Lockport, in the State of New 
York; it is asseciated in the same rock with the 
terebratula and several other fossils. 
The singular spinous projection from the tail of 
this Asaph, furnishes another analogy, between the 
trilobite and the limulus; an affinity which was sug- 
gested by Dr. Dekay; and which has been argued . 
with great ingenuity beth by himself and Professor 
‘Wahlenberg.* 
* See Nova Acta Regie Societatis Upsalensis : 1821. Aes. 
Annals of the Lyceum of Natural History. New York. Vol. i. 
pages 179—185. 
E 
