PEOF. E. W. CLATPOLE ON HELICOPORA. 33 



The above description was drawn up from an examination of 

 several (6 or 8) specimens. 



Horizon and locality. Upper beds of the Niagara (Wenlock) group 

 of the Upper Silurian at Cedarville, Greene Co., Ohio. 



Name derived from the spiral form and breadth of the polyzoary. 



The place where these specimens occur is at an outcrop of the 

 Upper Silurian rocks on the eastern slope of the Cincinnati arch, a 

 flexure in the strata, dating probably from late Cambro-Silurian 

 times. The beds of that formation there exposed are considered 

 nearly equivalent to the Guelph beds of Sir William Logan in 

 Canada. The fossils occur only in one layer in the quarry, and 

 often in nests. Very frequently, even in the same bed, none can be 

 found, their occurrence being extremely local and uncertain. In 

 some of the specimens four complete whorls of the spiral polyzoary 

 may be easily counted, separated from one another by about half 

 an inch of stone. 



The Corniferous Limestone of the Mississippi basin (Lower 

 Devonian) is one of the most fruitful fields for the palaeontologist. 

 Not only are fossils abundant on numerous horizons, but they are 

 often preserved with a perfection that brings out their minutest 

 details of structure. As its name implies, this group abounds in 

 flint, the silicified organisms of former times ; and even where purely 

 calcareous, as at the Falls of the Ohio, its Corals and Polyzoa cannot 

 be surpassed or equalled for beauty, unless it be in the localities to 

 be next mentioned. Accordingly the specimen about to be described 

 is not subject to the objections mentioned in the last description. 



Helicopoea Uleichi, n. sp. Plate IV. fig. 2. 



Sp. char. Polyzoary a thin spiral sheet of calcareous material, 

 somewhat thickened towards the base, the lowest part of which is 

 unknown, rising so as to make one turn of the spiral in an inch. 

 The frond makes an angle of about 35° with the imaginary axial 

 line in its lower portion. The angle is somewhat greater toward 

 the circumference, owing to a slight droop of the expanded sheet of 

 the polyzoary in its outer and thinner portion. Expanse of poly- 

 zoary unknown, but not probably exceeding an inch or two inches. 

 Axial edge considerably thickened and rounded, poriferous, but 

 without fenestrules. 



Inner face poriferous. 



Kays straight, ridged on the inner or front face, 50 in an inch, 

 not visibly striated, but striae may have been originally present ; 

 smooth and rounded on the outer or back surface, not ridged or 

 striated. 



Dissepiments or bars, on the front face rather lower than the 

 rays, and broader at their junction with them ; on the back of equal 

 height, and the rays smooth and rounded like them. 



Fenestrules 36 in an inch in length, but variable in size, not 

 extending through the polyzoary near the axial edge, and entirely 

 absent for about -^ of an inch from that line ; oval in front, at 



Q.J.G.S. No. 153. d 



