Contributions to Invertebrate Palaeontology. 515 



elevated above the cardinal border and ratlier inconspicuous, situated about 

 half or rather les^ than half the height of the shell from the anterior ex- 

 tremity, proportionally more distant on the larger specimens than on those of 

 small size. Hinge-line long and straight, extending four-fifths of the length 

 of the shell behind the beaks and characterized by a narrow but distinct 

 escutcheon. Anterior end short and full, very obtusely pointed at the longest 

 part, which is at about the middle of the height, above which point there is a 

 very distinct but narrow lunule extending to the extremity of the hinge-line. 

 Basal margin of the valve very broadly curved, slightly emarginate just ante- 

 rior to the middle and the whole subparallel to the cardinal line. Posterior 

 extremity sharply rounded below and the upper margin very obliquely trun- 

 cated ; body of the valve marked by a broad, distinct, mesial sulcus extend- 

 ing from behind the beak to the broad sinus of the basal margin. The um- 

 bonal ridge is rather sharply marked and angular in the upper portion, but 

 becomes less distinctly marked posteriorly ; postero-cardinal slope of moderate 

 width, very slightly concave in the younger stages of growth but less strongly 

 marked as the growth advances. Surface of the valves marked by strong, 

 sublamellose, concentric lines of growth jjarallel to the outer margin of the 

 valves. 



The shell undergoes considerable change in form and in the 

 strength of the surface characters between the younger and more 

 advanced stages of growth ; the sharpness of the features being 

 much reduced on the older portions, by the rounding of the umbo- 

 nal ridge and of the angularity of both the anterior and posterior 

 extremities of the shell. The shell differs in several of its external 

 features from the genus llodiolopsis, possessing a distinct lunule 

 and escutcheon as waW as the angular umbonal ridge, in all of which 

 features it corresponds with Goniophora. 



Formation and Locality. — In the hydraulic limestone of the 

 Lower Helderberg group at Peach Point, Put-in-Bay Island, Lake 

 Erie, and at Middletown, Marion Co., Ohio. 



ARTICULATA. 

 CRUSTACEA. 



M:EItOSrOJUATA. 



Genus EURYPTERU'S DeKay.' 



Eurypteriis Erieusis. 



Plate V, figs. 31, 32. 



Eurypterus Eriensis Whitf,, Ann. N. Y. Acad. Sci., March, 1882, p. 196. 



Among the fossils from the hydraulic limestones of Peach Point, 

 Put-in-Bay Island, Lake Erie, there are several detached cephalic 



