182 GASTEROPODS. 



Igoceras quincyense (MCCHESNEY). 



Plate liii, figs. lOa-b. 



Platyceras quincyense McChesney, 1861: Desc. New Foes. False. Rocks 



West. States, p. 90. 

 Platyceras quincyense McChesney, 1867 : Trans. Chicago Acad. Sci., vol. 



I, p. 46, pi. vi, figs. 6a-b. 

 Platyceras ( Orthonychia ) quincyense Meek & Worthen, 1868: Geol. Sur. 



Illinois, vol. Ill, p. 510, pi. xv, figs. 5a-b. 



PlatycerasguincyenseKeyeB, 1889: Proc. Acad. Nat. Sci., Phila., p. 290. 

 Capulus guincyensis Keyes, 1890: American Geologist, vol. VI, p 9. 

 Capulus quincyensis Keyes. 1890: Proc. Acad. Nat. Sci., Phila., p. 168, pi. 



ii,fig. 9. 

 Platyceras pettiense Miller, 1891: Geol. Sur. Indiana, 17th Ann. Rep., 



Adv. sheets, p. 81, pi. xiv, fig. 1. 

 Platyceras missouriensis Miller, 1891 : Geol. Sur. Indiana, 17th Ann. Rept. , 



Adv. sheets, p. 83, pi. xiv, fig. 2. 



Shell of medium size, broadly conical, often more or less 

 elongated ; expanding very rapidly and regularly from the cen- 

 tral or sub-central apex to the aperture. Usually five broad, 

 rounded ridges extend from near the apex to the aperture, which 

 is consequently more or less prominently quinquelobate ; the 

 ridges are not unfrequently further divided into two or more 

 smaller folds. Lip sharp, sinuous. Surface marked by sub- 

 imbricating lines of growth, and also by numerous small, often 

 undefined, longitudinal costse, which do not appear in the cast. 



Horizon and localities Burlington limestone : Burling- 

 ton ( Iowa ), Quincy ( Illinois ) ; Sedalia. 



The specimens described by McChesney and by Meek and 

 Worthen, were either exfoliated examples or internal casts ; 

 and this is the condition in which the species is usually found. 

 Owing to the peculiar state of preservation, the shells quickly 

 crumble away in handling, leaving only the internal casts, but 

 the distinctive quinquelobate character always renders them 

 easily recognizable. In the examples figured by McChesney, 

 and also by Meek and Worthen, the apices are wanting, but 

 the individuals were not as imperfect as was supposed. 



During the earlier period of their growth many of the 

 shells of I. quincyense were very broad, but when attaining 

 about one-third their maximum size, the aperture abruptly 



