April 0, 1877.] OZl [Hall. 



Contribution to Palceontology from the Museum of the Second Geological 



Survey of Pennsylvania. 



By Charles E. Hall. 



(Read befire the American Philosophical Society April 6, 18T7.) 



Genus Eurtpterus. 



Eurypterus ; Dekay, Annals of the Lyceum of Natural History of New 

 York, 1835, Vol. I, p. 375. 



The geological horizon of Eurypterus has heretofore been confined to 

 the Water-lime group, in the United States, although the genus has been 

 recently discovered in the English coal measures. 



The position of the Water-lime group is between the Onondaga salt 

 group and the Lower Helderberg group, therefore Upper Silurian. 



The Water-lime group in Pennsylvania is lithologically well defined, 

 but has not yet, to mj' knowledge, furnished a single specimen of Crus- 

 tacea. In New York the group is characterized by the crustaceans 

 Eurypterus, Pterigotus and Ceratiocaris.* 



Bernician. 



Eurypterus Pennsylvanicus (provisional, n. sp. ) 



In the collection of 1874, made under the direction of Mr. J. F. Carll, 

 in Venango County, Pa., a perfect but indistinct carapace of an Eurypterus 

 was found by his assistant Mr. Hatch. 



The specimen agrees in general with Eurypterus remipes of the Water - 

 lime. 



Position and locality, in sandy shale overlying a sandstone, which is 

 equivalent to the Garland Conglomerate, at Rooker Farm, Venango Co. 

 Pa. 



The horizon is in the transition series between tlie base of the Carbon- 

 iferous and the top of the Devonian. 



Carboniferous. 



Genus Eurypterus. 



Sub-genus Dolichopterus. 



Dolichopterus Mansfieldi. (n. sp.) 



Carapace semioral, wider than long, indented line visible along the 

 anterior margin, lateral margins nearly straight for one-fourth the length, 

 then evenly rounded ; eyes prominent, kidney-form, situated a little for- 

 ward of the centre of the carapace and about midway between a medial 

 line and the lateral margins. 



Body convex, the middle of the thorax slightly wider than the carapace, 

 length of the joints increasing towards the terminal spine-like prolongation. 

 * See N. Y. Paleontology, Vol. III. 



PROC. AMER. PHILOS. SOC. XVI. 99. 3z 



