HELICINIDAE 



39 



Family HELICINIDAE 



The family Hellclnidae is abundantly represented in tropical 

 countries, Mexico, Central America and the islands of the West 

 Indies. Though belonging to the Prosobranchiata, an order of 

 sea and freshwater snails, members of the Helicinidae are truly 

 terrestrial or land animals. Unlike the animals of Pulmonata, 

 the order of land snails common in Illinois, those of the 

 Helicinidae possess a horny operculum or lid with which they 

 may tightly close the shell against all intruders. Animals of 

 the Helicinidae have a rather long snout, truncated at the end, 

 and long, slender tentacles ; each eye is on a little swelling at 

 the outer base of a tentacle. 



Genus HENDERSONIA A. J. Wagner 



The only genus of the family Helicinidae found in Illinois, 

 Hendersonia is known in the United States, China and Japan. 

 All of the shells are similar to that of Hendersonia occulta. 



HENDERSONIA OCCULTA (Say) 



The reddish or yellowish shell of Hendersonia occulta is 

 very thick, and its surface is marked by fine, curved ribs. It 

 measures about one-fourth inch (5-7 mm.) in diameter. The 



spire, which is dome shaped, has 

 6^/2 whorls. The periphery of the 

 \N^'xi^^' body whorl is made angulate by 



the presence of a relatively sharp 

 carina which borders the sutures 

 on the spire whorls. The base of 

 the shell is rounded and is without 

 an umbilical opening. The aperture 

 is lunate in shape, and the outer 

 lip is greatly thickened, forming a heavy projecting ridge. Only 

 the adult shell has this ridge. 



This snail, formerly named Helicina occulta, is now very 

 rare in Illinois, and is at present known only from near Athens, 

 IVIenard County. It may be found in dry well-wooded places 

 under and about forest debris. Though rare in Illinois as a 

 living member of the fauna, it is very abundant in fossil 

 deposits of the last geological period. 



