DESCRIPTIONS OF SPECIES. 



SPECIES FROM THE HYDRAULIC LIMESTONES OF THE 

 LOWER HELDERBERG GROUP. 



MOLLUSCOIDEA. 

 BRACHIOPODA. 



Genus STREPTORHYNCHUS King. 



Streptorhynchus hydraulicum. 



Pi,ate I, figs. 1—3. 



Streptorhynchus hydraulicum Whitf., Ann. N. Y. Acad. Sci., 1882, p. 193. 



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

 eighths 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 

 length, 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 depression 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 strioe, which are distinctly alternating in size; 

 the principal ones proportionally very strong. 



The small size of the shell, with the strong radiating and alternate 

 striae, 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 presents much more the features of forms of the 

 genus from the Coal Measures than any heretofore described from Silur- 

 ian rocks of America, and will not be readily confounded with any known 

 species. 



Formation aud Locality. — In the hydraulic beds of the Lower Helder- 

 berg group, at Belleville, Sandusky county, and at Greenfield, Ohio; 

 associated with Meristella bella, Nucleospira rotundata and Leperditia alta, 

 occurring sometimes in great numbers, almost covering the surfaces 

 of slabs. 



