174 PROCEEDINGS OF THE ACADEMY OF [1890. 



lington limestones are much more intimately related biologically than 

 had hitherto been generally regarded ; and that many so-called 

 Keokuk species are merely the subsequent genetic representatives of 

 Burlington forms. The validity of their distinction simply on ac- 

 count of occurring in differently named geological horizons cannot 

 be sustained. It is not to be supposed that the biologic sequence of 

 two divisions as the Burlington and Keokuk, so closely related 

 stratigraphically and lithologically, and deposited under identi- 

 cal quiet conditions should ])e so widely separated faunally as the 

 described species from these limestones would indicate. 



Capulus infundibulum (Meek & AVorthen). [Plate II, fig. 10.] 



Platyceras subrechitn Hall, 1859. Geol. Iowa, vol. 1, pt. ii, Supp., p. 89 (not 

 P.subrectum Hall, 1859, for a New York specimen). 



Platycems subrectum Hail, 1860. Twelfth Am. Reg. Rept. Univ. N. Y., p 18. 

 (Not P. subrectuvi Hall, 1859.) 



Platyceras infundibulum Meek & Worthen, 1866. Proc. Acad. Nat. Sci., Phila., 

 1866, p. 1266. 



Platyceras infundibulum Meek & Worthen, 1873. Geol. Sur. Illinois, vol. V, 

 p. 517, pi. XVII, fig. 3. 



Platyceras infundibulutn Keyes, 1888. Proc. Am. Philosophical Soc, vol. XXV, 

 p. 238, fig. 1. 



Platyceras infundibuhan Keyes, 1889. Proc. Acad. Nat. Sci., Phila., 1889, p. 

 289. 



Capulus infmdibuluvi Keyes, 1890. Am. Geologist, vol. V. 



Shell more or less conical, often somewhat oblique, with usually 

 many undefined longitudinal folds; apical portions slender, expand- 

 ing regularly at first and then more rapidly. Apex attenuated, 

 often slightly deflected toward the posterior side. Surface smooth, 

 but toward the aperture marked by numerous undulating, fre- 

 quently imbricating lines of growth. 



Horizon and localities. Keokuk limestones and shales : Keokuk, 

 Iowa ; Warsaw, Illinois ; Crawfordsville, Indiana. Burlington 

 limestone : Burlington, Iowa. 



The most closely allied form associated with this species is C.fis- 

 surella (Hall), from which it is distinguished in being proj)ort ion- 

 ally more elongate, while the apical part of the shell is character- 

 istically slender. Ordinarily the shell is more or less conspicuously 

 plicate, but the folds are, for the most part, narrow, and usually ir- 

 regular and broken. 



For an elongated specimen Meek & AVorthen' have indicated the 

 nume J^latyceras extinct or " shon\d it prove distinct,'' but the term 



1 Proc. Acad. Nat. Sci., Phila., p. 266, 1866. 



