Weller — KinderJiook Faunal Studies. 459 



Aperture subcircular, the outer lip thin, the inner lip thick- 

 ened by a flat callosity upon the columella. Surface marked 

 by very fine transverse lines of growth. 



The dimensions of an average individual are : height 7.25 

 mm., maximum diameter 7.25 mm., width of aperture 5 mm,, 

 height of aperture 5.5 mm. 



Remarks. This is a common species in the fauna and may 

 be easily distinguished from other members of the genus by 

 reason of its small size, the small number of volutions, and 

 the ventricosity of the outer volution. 



Platyceras erectoides n. sp. 



Plate 2, figs. 34-35. 



Description. Spire close coiled at the apex for about one 

 and one-half volutions, beyond which the body volution is 

 free ; somewhat rapidly expanding, often more or less spread- 

 ing near the aperture. Aperture subcircular, subovate or 

 subelliptical in outline, usually more or less sinuate. Dorsum 

 rounded or subangular, the two sides of the shell usually 

 nearly equal. Surface marked by fine, closely arranged, 

 undulating lines of growth which are not conspicuously 

 lamellose. 



The dimensions of an average specimen are ; height 15 mm., 

 length of aperture 14 mm., width of aperture 18 mm. 



Remarks. This species is sufficiently distinct from all the 

 Kinderhook and other Mississippian members of the genus, 

 but it closely resembles P. erectum Hall, of the New York 

 Hamilton fauna. The Glen Park specimens seem to agree 

 exactly with this Hamilton species in general form and pro- 

 portions, although it seems never to grow so large as that 

 species. The only difference between the two shells which 

 seems to be of specific value, is the lack of conspicuously 

 lamellose lines of growtii in the Missouri shell. This char- 

 acter seems to be a good one as the shells apparently have 

 not been water worn or eroded. 



Platyceras evolutus n. sp. 



Plate 2, figs. 32-33. 



Description. Shell small, arcuate, the apex oblique and 



