GASTEEOPODS. 163 



Raphistoma subplana SHUMARD. 



Raphistoma subplana Shumard, 1863: Trans. St. Louis Acad. Sci.,vol. 

 II, p. 106. 



Shell depressed, turbinate; width rather more than one - 

 third the height ; whorls about four, periphery of last one 

 sharply angular, inner edge obtusely angulated; upper sur- 

 face subplane, with a shallow groove just within the exterior 

 margin ; under surface convex ; umbilicus small ; aperture 

 transverse, subtrigonal. Width 41 lines, height 3 lines. (Shu- 

 mard.) 



Horizon and localities. Cambrian limestone : Ozark 



county. 



( 

 Raphistoma lenticularis (CONRAD). 



Pleurotomaria lenticularis Conrad, 1842: Emmon's Geol. Rep, New York, 



p. 392, fig 2, and p. 293, figs. 2, 3. 

 Pleurotomaria lenticularis Owen, 1844: Geol. Expl. Iowa, Wise, and 111., p. 



86, pi. x via, fig. 6, 



Raphistoma lenticularis Walter, 1859: Canadian Org. Rem., Decade 1, p. 12. 

 Raphistoma lenticulrris Hall, 1862: Geol. Sur. Wisconsin, p. 39, fig. 4. 

 Raphistoma lenticularis Meek & Worthen, 1868 : Geol. Sur. Illinois, vol. Ill, 



p. 316, pi. ii, fig. 7b. 



Shell lenticular, the breadth being about twice the height, 

 nearly equally convex above and below ; whorls four to five in 

 number, flattened above, sharply carinate around the periphery, 

 and rather convex below; suture not well defined ; umbilicus 

 broad ; aperture rhomboidal in outline. Surface unknown in 

 Missouri specimens. 



Horizon and localities Lower Silurian, Trenton lime- 

 stone : McCune ( Pike county ). 



Mad urea magna (Ls SUEUR). 



Plate lii, figs. 9a-b. 



Maclurites magna Le Sueur, 1818 : Jour. Acad. Nat. Sci., Phila., vol. I, 



p..312, pi. xiii, figs. 1-3. 

 Maclurea magna Hall, 1847: Pal. New York, vol. I, p. 26, pi. V, figs. 



la-d. 



Shell rather large, composed of three or more volutions, 

 rapidly increasing in size; flattened above, rounded and car- 

 inated below. Surface marked only by lines of growth. 



