190 GASTEROPODS. 



Orthonychia acutirostre (HALL). 



Plate liv, figs. 2a-c. 



Capulus acutrostris Hall, 1856: Trans. Albany Inst.,vol. IV, p. 31. 

 Capulus acutirostris Hall, 1858: Geology Iowa, vol. I, p. 665, pi. xxiii, 



figs. 14a-b. 

 Platyceras (Capulus) acutirostris McChesney, 1860: Desc. New False. Foss. 



West. States, p. 71. 

 Platyceras uncum Meek & Worthen, 1866: Proc. Acad. Nat. Sci., Phila., 



p. 264. 

 Platyceras uncum Meek & Worthen, 1873: Geol. Sur. Illinois, vol. V, p. 



516, pi. xvii, fig. 1. 

 Platyceras acutirostris Whitfield, 1882: Bui. Am. Mus. Nat. Hist., vol. I, 



p. 67. 

 Platyceras acutirostris Hall, 1883: Geol. Sur. Indiana, p. 370, pi. xxxi, 



figs. 13-15. 



Capulus acutirostris Keyes, 1890: Am. Geologist, vol. VI, p. 9. 

 Capulus acutirostris Keyes, 1890: Proc. Acad. Nat. Sci. , Phila. , p. 170. 



Shell below medium size, rather slender, strongly arcuate, 

 forming from one to one and one -half volutions; posterior 

 side for some distance from apertural margin nearly straight. 

 Spire laterally more or less compressed ; sometimes small and 

 short, sometimes long, attenuate, simply incurved or enrolled. 

 Aperture oval, or sub-circular; margin sharp, sinuous. Surface 

 marked by somewhat imbricated lines of growth, and several 

 obscurely defined longitudinal plications, the anterior one be- 

 ing usually larger than the others, and often forming a promi- 

 nent subangular ridge. 



Horizon and localities. Keokuk limestone and shales : 

 Warsaw and Nauvoo, Illinois ; Saint Louis limestone : Spur- 

 geon Hill and Bloomington, Indiana; Tuscumbia, Alabama. 



This form appears to have a geographically wide distribu- 

 tion ; and it also presents considerable variation, even within 

 limited areas. It was originally described from Spurgeon Hill, 

 Indiana, and like all the faunal remains of that locality is char- 

 acteristically depauperate. Platyceras uncum M. & W. seems 

 to be identical with this species, the imposed conditions of en- 

 vironment being more favorable to a normal development, and 

 to the attainment of somewhat larger proportions. 



