EURYPTERITS. PPP. 31 



the important members and appendages of the animal, the 

 body is sufficiently well-preserved to distinguish the spe- 

 cies, which is also characterized by the ornamentation of 

 the joints of the swimming limbs. The occurrence of crus- 

 taceans of this character, in these rocks, is so rare that 

 ever}^ specimen is of importance. 



E. Pennsylvanicus is a smaller and more fragile form ; 

 they cannot be directlj^ compared on account of the imper- 

 fection of the material. 



Formation and locality. Chemung group; Warren, Pa. 



EUEYPTERUS PENJSrSYLVAlSriCUS. 



Plate V, Fig. 18. 



Eurypterus Pennsylv aniens, C. E. Hall, Proc. Am. Phil. Soc. ; Vol. VII, 



p. 621, 1877. 



Carapace semi-circular ; length a little more than half the 

 breadth , post-lateral angles mucronate. 



Eyes situated on the anterior half of the carapace, sepa- 

 rated by a distance equal to about one-half the breadth of 

 the head. Midway between the eyes is a small flat node or 

 elevation, on each side of which is a larger longitudinal 

 prominence. There are also two similar nodes above the 

 posterior margin. The posterior angles show two oblique 

 short ridges. These elevations of the carapace probably 

 indicate the positions of internal organs and the points of 

 attachment of muscles. 



The surface ornaments are not well-preserved, the speci- 

 men shows numerous small tubercles, esjDecially over the 

 posterior portion. 



The carapace has a length of 8.5 mm. and a breadth of 

 15 mm. 



The shape of the carapace and rlie arrangement of the 

 nodes is quite different from E. Manftfiddi, and tlie geo- 

 logical i)Osition is considerably higher in tlie series than E. 

 Beecheri. 



IPorniatiou and locality. \\\ an arenaceous shaln ; at 

 Rooker farm, Pithole City, Venango Co., Pa. 



