'460 Trans. Acad. Sci. of St. Louis. 



incurved nearly in the plane of the right side of the shell, 

 with the first volution or volution and one-half close coiled; 

 gradually expanding from apex to aperture ; dorsum sharply 

 rounded or subangular, the free portion of the shell obliquely 

 compressed. Aperture narrowly subelliptical in outline, more 

 or less sinuous. Surface marked with more or less irregular 

 non-lamellose lines of growth. 



The dimensions of a nearly complete specimen are : height 

 8 ram., maximum diameter of aperture 6 mm., minimum di- 

 ameter of aperture 4 mm. 



Remarhs. This species is quite distinct from any of those 

 members of the genus which have been described from the 

 Kinderhook faunas, but it is closely allied to the Hamilton 

 species P. thetis Hall. The Glen Park specimens are smaller 

 than those of the Hamilton fauna and lack the conspicuous 

 lines of growth. The most notable difference, however, is in 

 the oblique compression of the free portion of the shell and 

 the consequent narrowly elliptical outline of the aperture, the 

 aperature of P. thetis being '• nearly round or subquadran- 

 gular." 



PlATYCERAS QLENPARKEN8I8 U. Sp. 



Plate 2 f figs- 30-31. 



Description. Shell below medium size, strongly com- 

 pressed, rapidly expanding from apex to aperture; the apex 

 incurved, lying nearly in the plane of the right side of the 

 shell, the first one or one and one-half volutions closely 

 coiled, the dorsum sharply rounded or subangular; the aper- 

 ture narrowly subelliptical in outline, more or less sinuous. 

 Surface marked by irregular, nonlamellose lines of growth, 

 sometimes formino; wrinkle-like constrictions of the shell. 



The dimensions of a large individual are: height 9 mm., 

 maximum diameter of aperature 10 mm., minimum diameter 

 of aperature 5.5 mm. 



Remarks. This shell has somewhat the aspect of the spe- 

 cies that has been described as Strophostylus broadheadi 

 S. A. M., from the Chouteau limestone of central Missouri, 



