GASTEROPODS. 199 



by numerous small, short, equidistant costae parallel to the 

 lines of growth; the surface otherwise glabrate. 



Naticopsis ventricosa (NORWOOD & PRATTEN). 



Natica ventrica Norwood & Pratten, 1854: Jour. Acad. Nat. Sci., Phila., 

 (2), vol. ILL, p. 76, pi. ix, fig3. lOa-b. 



Naticopsis magister Stevens, 1858: Am. Jour. Sci., (2), vol. XXV, p. 261. 



Naticopsis pried Shumard, 1858: Trans. St. Louis Acad. Sci., vol. I, p. 202. 



Natica shumardi McChesney, 1860: Desc. New Pal. FOBS., p. 62. 



Natica altonensis McUhesney, 1860: Desc. New Pal. Foss., p. 63. 



Naticopsis shumardi McChesney, 1867: Trans. Chicago Acad. Sci., vol. I, 

 p. 49. 



Naticopsis altonensis McChesney, 1867: Trans. Chicago Acad. Sci., vol. I, 

 p. 50, pi. ii, fig. 14. 



Naticopsis ventricosa Meek & Worth en, 1873: Geol. Sur. Illinois, vol. V, 

 p. 592, pi. xxviii, fig*. 13a-b. 



Naticopsis altonensis Meek & Worthen, 1873- Geol. Sur. Illinois, vol. V, 

 p. 595, pi. xxviii, figs, lla-b. 



Naticopsis altonensis, var. gigantea Meek & Worthen, 1873 : Geol. Sur. Illi- 

 nois, vol. V, pi. xxviii, figs. 12a-b. 



Shell ovoid ; spire small, depressed ; volutions two or 

 three, the last one very large and ventricose, regularly rounded, 

 except near the suture, where it is slightly flattened or concave. 

 Suture deeply impressed toward the aperture, which is oval, 

 compressed above ; labrum sharp ; columellar lip thick, smooth. 

 Surface marked by fine lines of growth, which, near the suture, 

 pass into small, well-defined, rounded ridges. 



Horizon and localities. Upper Carboniferous, Upper Coal 

 Measures : Kansas City, Clinton ( Henry county). 



Genus Trachydomia MEEK & WORTHEN. 



The term Trachydomia was originally proposed by Meek 

 & Worthen in 1866, as a subgenus of Naticopsis McCoy. It is 

 now believed that the characters are sufficiently well marked 

 to admit of a distinct generic separation from McCoy's genus. 



In contradistinction to Naticopsis the shells of Trachydo- 

 mia are massive, with the spire larger and more elevated ; the 

 outer lip very thick, but abruptly becoming sharp ; the colu- 

 mella very heavy, the callosity thick and greatly extended; the 

 volutions shallowly channeled along the suture ; and the sur- 

 face covered with numerous small equidistant nodes. But 

 two North American specimens Littorina wheeleri Swallow 



