36d TWENTIKill REPORT ON THE STATE CABINET. 



GASTEROPODA. 



GENUS PLEUROTOMARIA. 



PLEUROTOMARIA HOYI. 



PLATE 15 (6), FIG. 10. 



PIcurotoinaria hoyi : Hall, Geol. Survey of Wisconsin; Report of progress, p. 35, 

 1801. 



Shell broadly depressed-conical, the spire moderately elevated, consisting 

 of about four volutions which are gradually enlarged from the apex, the 

 last one becoming slightly ventricose toward the aperture. Volutions 

 flattened upon the upper side, and the entire height of each one showing 

 above the other ; periphery somewhat flattened, with a depressed band 

 truncating the upper angle. Lower side of volutions flattened, except 

 the outer half of the last one, which is rounded toward the aperture, and 

 abrubtly descending into the wide umbilicus. 



Surface finely striated on the lower side of the volution, with a deep 

 retral curve on the band, where the striag are somewhat fasciculate. The 

 periphery of the cast is sometimes marked by three or four strong but 

 obscure striae below, and parallel to the revolving band. 

 This species resembles P. umhilicata of the Trenton limestone, but the 



volutions are more elevated above each other, and the upper surface is 



wide and flat. 



FoTmation and locality. Limestone of the Niagara group, at Racine, 



Wisconsin. 



PLEUROTOMARIA OCCIDENS (n. s.). 



PLATE 15 (6), FIGS. 11 & 12. 

 Pleurotomaria labrosa, var. occidens : page 343 = p. 39 original paper. 

 A further study of the specimens of this species has shown the necessity 

 of an entire separation of this form from the P. labrosa of the Lower 

 Helderberg group. In some larger specimens the vertical height of the 

 outer volution is shown to be much less than in P. labrosa, while the 

 columellar lip has never been so much thickened. 



PLEUROTOMARIA HALEI. 



PLATE 15 (6), FIGS. 13 & 14. 



Pleurotomaria halei : Hall, Report of Progress GeoL Survey of Wisconsin, p. 34, 1861. 



Shell suborbicular, the spire moderately ascending, the height equal to a 

 little more than two-thirds the greatest diameter, consisting of three or 

 four volutions which are rounded on the top, and expanding somewhat 

 rapidly in size ; the last one quite ventricose, and in the cast is sub- 

 angular on the periphery : the under side of the last volution is rounded 

 from the edge into the rather large umbilicus. 



