39 I PALJ:0NT0L0GY of new- YORK. . 



'* of appendages, of which the hinder were dilated for swimming" ; and 

 the illustrations by M. Eichwald of the Russian species, and the observa- 

 tions of Professor M'Coy, show that the number and character of these 

 appendages were similarly regarded by them all*. 



Fortunately I am able, in three distinct species, to show that the 

 Eurypterus was possessed of five pairs of appendages or organs of sense 

 and motion ; the four posterior pairs being those seen by Dr. Dekay, 

 while the anterior pair, being a little shorter, though similar to the two 

 next, are rarely seen. This number being established for three species, 

 we may presume that it is a feature of generic importance, and that the 

 descriptions which recognize the existence of three pairs only have arisen 

 from imperfect specimens. 



The articulation of these appendages has never been clearly shown in 

 any of the figures which have fallen under my observation ; the original 

 figure of Dr. Dekay being indeed better than any subsequent one, though 

 that by Dr. Harlan gives a better knowledge of the fourth pair (third of 

 Dekay), the number of articulations being correctly represented. The 

 figure of Dr. R(emek, though of a very large and beautiful specimen, has 

 failed to exhibit the true structure of these appendages. 



Since the descriptions were written and the preceding pages in type, 

 wishing to present the opinion of the highest authority in regard to the 

 zoological affinities of these fossils, I have submitted the collection of 

 specimens of Eurypterus in my possession to the examination of Professor 

 Agassiz. This pre-eminent naturalist has given his opinion most unequi- 

 vocally that the Eurypteri are closely related to Limulus, belonging even 

 to the same order. He regards the antennal system as entirely absent. 

 The organs of locomotion all belong to the cephalic region ; and while 

 externally they perform the functions of feet, they are at their bases 

 organs of manducation. The central organ, indicated as a locomotive 

 appendage, and attached to the lower side of the first segment, Professor 

 Agassiz regards as similar to the appendage attached to the membrana- 



I regret that I have not been able to see the illustrations of Professor Eichwald, referred to above. 



