FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 185 



Platyostoma turbinata, var. cochleata. HALL. 



Platyostoma hirbinata, var. cochhata, Hall. Illust. of Devonian Fossils, Caster., pi. 10 187G. 

 Platyostoma turbinata, var. cochleata, Hall. Pal. N. Y , Vol. 6, part 2, p. 281879. 



Shell turbinate. Spire elevated, conical ; volutions about four or five ; per- 

 iphery of the last volution obtusely rounded or distinctly sub-angular, with 

 a sinus in the margin of the aperture ; the last volution sometimes becoming 

 free near the aperture, which latter is obliquely sub-ovate or ovate ; peristome 

 sinuous, often with a deep notch in the upper margin, and sometimes con- 

 tinued in a columellar extension below. 



The specimens referred to this variety all agree in having an elevated spire, 

 with rounded volutions above the last one, which is almost invariably sub- 

 angular. 



Formation and Locality. Found associated with Plat, lineala in the rotten hornstone of the Devo- 

 nian formation around Louisville, Ky. 



Platyostoma niagarense. HALL. 



Plate XXXIII., figure 30. 



Platyostoma niagarenm, Hall. Pal. N. Y., Vol. 2, p. 287, pi. 60, figs, la-lv 1852. 

 Platyostoma niagarense, Hall. 28th Rep. N. Y. St. Mus. Nat. Hist., Mus. edit., p. 175, pi. 28, figs. 1-12; pi. 



29, figs. 1-151879. 

 Platyostoma niagarnwe, Hall. Ind. Geo. Survey, llth Rep., pi. 29, p. 3181881. 



The following description is quoted from Prof. Hall : Shell ovoid or sub- 

 globose ; volutions three to four, the last one very ventricose ; spire varying 

 from the plane of the outer volution to an elevation of one-fifth or one-fourth 

 the height of the shell above. 



Apex minute, somewhat rapidly expanding, the first two volutions usually 

 symmetrical ; the outer volution often unsymmetrical, very ventricose and 

 regularly rounded upon the back, but not unfrequently extended and becoming 

 free towards the aperture, and marked on the upper or lower side, or upon 

 both, by a groove, along which .the striae are abruptly bent, indicating a sinus 

 in the peristome during some period of its growth ; peristome entire or undu- 

 lated, sometimes distinctly notched in the margin, free or adhering on the 

 columellar side, and sometimes expanded and presenting a thickened callosity 

 or oolumellar lip. 



Surface marked by fine undulating striae of growth, which sometimes become 

 lamellose. In well preserved specimens, finer revolving striae cancellate the 

 striae of growth, and sometimes the surface is marked by revolving ridges. 



Formation and Locality. Occurs in the Niagara near Louisville, Kentucky. The specimen 

 figured is a, very young one. 

 OEOL. SUK. 24 



