508 Contributions to Invertebrate Palaeontology. 



DESCRIPTIONS OF SPECIES. 



SPECIES FROM THE HYDRAULIC LIMESTONES OF THE 

 LOWER IIELDERBERG GROUP. 



MOLLUSCOIDEA. 



BRACHIOPODA. 



Genus STREPTORHIWCHUS King. 



Streptorhyncliiis Uydrauliciim. 



Plate V, figs. 1-3. 



Streptorlnjnchus hydrauUcum Whitf., Ann. N. Y. Acad. Sci., 1SS2, p. 193. 



Shell small to minute, the largest individuals yet observed not exceeding 

 five-eightlis of an inch in greatest diameter, while the most of those observed 

 are not more than two-thirds as great. Valves depressed convex, or, more 

 commonly, appearing very flat, as seen on the surface of the stone. Hinge- 

 line straight, nearly as long as the width of the shell below, and the latter 

 usually more than the lengtli, frequently nearly once and a half as great. 

 Ventral valve characterized by a very narrow and nearly vertical cardinal 

 area, and a usually more or less twisted or otherwise distorted beak. Dorsal 

 valve slightly more convex than the ventral, with a perceptible mesial depres- 

 sion extending from beak to base, becoming broad and undefined below the 

 middle of the length. Surface of the shell marked by coarse and somewhat 

 rigid radiating striiie, whicli are distinctly alternating in size ; the principal 

 ones proportionally very strong. 



The small size of the shell, with the strong' radiating and alter- 

 nate striic, are distinguishing features of the species. There is no 

 species resembling it, to any degree, among- the fossils of New York 

 rocks of a corresponding age. It i>resents much more the features 

 of forms of the genus from the Coal Measures than ;my heretofore 

 described from Silurian rocks of America, and will not be readily 

 confounded with any known species. 



Formntion and Localiti/. — In the h3'dranlic beds of the Lower 

 llelderberg group, at Belleville, Sandusky County, and at Green- 



