34 



PE0F. E. W. CLAYPOLE ON HELICOPOEA. 



back nearly round, and towards the axial edge represented by 

 narrow false fenestrates, some of which measure T \j of an inch in 

 length, retaining the usual width. 



Pores circular, usually three, often four, on each side of a fenes- 

 trate, distant about their own diameter ; the highest and lowest 

 are often situated in the angle between the ray and the dissepiment. 



Horizon and locality. The Upper Helderberg or Corniferous 

 Limestone, at the Falls of the Ohio, near Louisville, Kentucky. It 

 was found by Mr. E. 0. Ulrich, of Cincinnati, after whom I have 

 consequently named the species. 



This species is exceedingly different in appearance from H. lati- 

 spiralis, in consequence of its small size, the nearly upright position 

 of the spiral expanded polyzoary, and the rapid ascent of the spiral ; 

 but it agrees with that species in all its generic characters, absence 

 of axis, and spiral growth. 



It is an exceedingly beautiful little species, of which, however, I 

 know no other specimen than that here described ; but this is so 

 well preserved that little or nothing remains to be desired for com- 

 pleting the specific description of all the parts that are present. 



This fossil is interesting, as it shows the continuance of the spiral 

 form from the Silurian (Niagara) system, in which H. latispiralis 

 occurs, into the Devonian, not apparently as a deformity or sport, but 

 as a normal habit of growth. Its minuteness is striking compared 

 with the comparatively enormous size of its Silurian predecessor. 

 This is plainly shown in the figures, where, though enlarged to 

 double its actual size, it looks but a pigmy beside the larger and 

 older species. 



The Lower Carboniferous Limestone of the Mississippi basin, from 

 which the species next to be described was obtained, equals or, if 

 possible, in some respects surpasses the Corniferous Limestone in 

 the quantity and beauty of its organic remains, especially Crinoids 

 and Polyzoa. Its fossils, too, are equally well preserved The fine- 

 ness of the material has moulded their minutest details cf structure, 

 and the absence of acidulated water has prevented their destruction 

 or incrustation. 



Helicopoka akchimedifoPvMis, n. sp. Plate IV. figs. 3, 4. 



Sp. char. Polyzoary a thin calcareous spiral sheet, very much 

 thickened at the basal or axial portion, rising so as to form one turn 

 of the spiral in an inch, and making with the imaginary axial line an 

 angle of about 35°. Expansion of the polyzoary unknown, but probably 

 not large. Only two small fragments of the thin and expanded 

 portion are preserved in the only specimen known to me, from 

 which this description is compiled. 



Lower or inner edge of the polyzoary considerably thickened, and 

 forming a distinct rounded edge. It does not, however, form an 

 axis, but itself runs up spirally round the place where a solid axis 

 would be if it were present. It measures one tenth of an inch in 

 thickness, and is finely striated longitudinally. 



