822 NORTH AMERICAN INDEX FOSSILS. 



Family Zonithxe. 

 CCXVIIL Arch^eozonites Sandberger. 

 Thick-shelled, globose, Helix-like shells, with rather high spire, 

 and deep umbilicus ; outer lip sharp ; surface smooth. Carbonic- 

 Miocenic. 



699. A. priscus Dawson. (Fig. 1208, h,i.) Carbonic. 

 Small; spire rather low and broad; whorls compound and 



rounded ; surface with fine growth lines. 

 Coal measures of Nova Scotia (Joggins). 



Family Helicid^e Keferstein. 

 CCXIX. Helix Linne. 

 Generally thin-shelled, of several whorls, more or less regularly 

 increasing, flat- or low-spired (obtuse) ; aperture incomplete, with 

 disconnected margin; umbilicus present or absent; lip simple or 

 with terminal varix. Many subgenera are recognized. More than 

 3,400 species. Terrestrial. Eocenic-Recent. 



700. H. leidyi Hall and Meek. (Fig. 1209, c, d.) Miocenic. 

 High-spired; apical angle approaching 90 . Many whorled; 



body whorl subglobose. 



701. H. diespiter Dall. Pliocenic. 

 Many-whorled, low-spired ; base horizontally flattened ; umbilicus 



small, partly covered; oval aperture with pronounced expansion, 

 where lip joins body whorl; a terminal deflection or varix. 

 Silex bed of Ballast Point, Florida. 



702. H. crusta Dall. Pliocenic. 

 Smaller with umbilicus less covered, aperture smaller and 



less oval. 



Associated with preceding. 



703. H. (Polygyra) albolabris (Say). Pleistocenic-Holocenic. 

 Larger than preceding, non-umbilicate ; spire low, finely striate ; 



lip sharply reflected ; strong umbilical covering. 



Loess of southern Mississippi Valley; living in eastern North 

 America. 



704. H. (Pyramidula) alternata (Say). Pleistocenic-Holocenic. 

 Low-spired, deeply and broadly umbilicate, with 5 or more 



whorls, with sharp growth lamallae above, smooth below, last one 



