GASTEROPODS. 181 



Shell like C. tribulosus (White), but without spines, and 

 with the apex inclined quite noticeably to the right. 



Horizon and localities Upper Carboniferous, Upper Coal 

 Measures : Kansas City. 



A careful comparison shows the form described from Ne- 

 braska by Meek is only a more matured individual of C.parvus. 

 Since, however, Swallow's species was poorly denned and was 

 never figured, and as Meek was the first to give a clear diag- 

 nosis of this form, both by a full description and by good illus- 

 trations, it is, perhaps, questionable whether Meek's name 

 should not really be retained for the form, Platyceras nebrascense 

 having been almost universally applied to this species as oc- 

 curring throughout the West. 



Genus IGOCERAS HALL. 



The reasons for reviving HalPs generic term Igoceras have 

 already been stated fully elsewhere. It is proposed to apply 

 the name only to certain more or less distinctly conical shells 

 which were originally under Conrad's abandoned genus Platy- 

 ceras. The following American species may be considered as 

 properly belonging here : 



Platyceras conicum, Hall. P. subplicatum, Meek & Worthen. 



P. perplexum, Hall. P. quincyense, McChesney. 



P. plicatum, Halli P. fissurella, Hall. 



P. pyramidatum, Hall. P. pabulocrinus, Owen. 



P. capulus, Hall. 



Igoceras pyramidatum (HALL). 



Platyceras pyramidatum Hall, 1859: Pal. New York, vol. Ill, p. 336, pi. 



Ixiv, figs. 7, 9. 

 Platyceras pyramidatum Meek & Worthen, 1868: G-eol. Sur. Illinois, vol. 



Ill, p, 3S9, pi. vii, fig. 11. 



Shell much like that of I. pabulocrinus, but more ventri- 

 cose, and the sides convex instead of nearly straight. 



Horizon and localities. Upper Silurian limestone : Bai- 

 ley landing (P^rry county). 



