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 

 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 associated 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. Dekayj and which has been argued 

 with great ingenuity both by himself and Professor 

 Wahlenberg.* 



'* See Nova Acta Regise Societatis Upsalensis: 1821. Also, 

 Annals of the Lyceum of Natural History. New York. Vol. i. 

 pages 179185, 



