INVERTEBRATES. 303 



This species is evidently closely related to Eumphalus pentangulatus of 

 Sowerby (Mm. Con., i, p. 97, pi. 45, fig. 1 and 2), but is smaller, and differs 

 in having the angle on the upper side of the whorls located nearer the outer 

 margin. Its periphery is also much less prominently rounded, its whorls less 

 rounded below, and its umbilicus proportionally deeper. 



We find these differences particularly in the position of the angle on the 

 upper side of the inner whorls, and the less prominently rounded side of the 

 body whorl in our shell, quite obvious on comparison with authentic specimens 

 of E. pentangulatus, from Ireland. 



Our species seems to be also very near, if not really identical with a form 

 subsequently described by Prof. Swallow, from the same horizon, under the 

 name Euomphalus perspcctwus (Trans. St. Louis Acad,, Hay, 1862). A draw- 

 ing, however, of Prof. Swallow's shell, shown one of us by him, represents 

 much stronger marks of growth than we have yet seen on our species. 



Locality and position: Thompson's quarry, Randolph county; Chester group 

 of Lower Carboniferous series. Also, in the same position in Saint Genevieve 

 county, Missouri. 



Genus PLEUKOTOMARIA, Defrance; 1826. 



(Diet. Sci. Nat, xli. tab.'86.) 



Pleurotomaria chesterensis, M. and W. 



PI. 24, fig. la, 16, \c. 



Pleurotomaria chesterensis, Meek and "Worthbn, October, 1860. Proceed. Acad. Nat. 

 Sci., Philad., p. 460. 



Shell of medium size, turbinate; spire moderately elevated; 

 volutions about six, convex, distinctly carinated around the 

 middle, and flattened or concave above and below the carina, 

 the flattened space above being oblique, and that below verti- 

 cal; last whorl provided with a second carina below the first, 

 and slightly convex on the under side ; suture linear ; umbili- 

 cal perforation small, or nearly closed ; aperture subquadran- 

 gular, and a little wider than high ; spiral band occupying the 

 middle of the vertically flattened space between the two carinse 

 on the body whorl, and passing around about half-way between 



