64 ZONITIDAE 



Family ZONITIDAE 



To the family Zonitidae belong several species of snails 

 having yellowish, horn-colored or hyaline shells with a glassy or 

 shining surface. They vary in size from less than one-sixteenth 



inch to 1 inch (1.5-26.0 mm.) in diameter. The peristome of 

 the aperture is always simple and sharp, never reflected as is 

 that of the Polygyridae. The surface sculpture is nearly always 

 fine and seldom appears as riblets. 



The shell at times completely covers the large animal, which, 

 however, is well extended from its horny covering when in loco- 

 motion. The body and foot of the animal are about twice as 

 long as the diameter of the shell. The eye peduncles are long 

 and slender, the tentacles short. The figure illustrates the 

 animal and shell of Mesomphix cupreus, a species of this family. 



The Nearctic Zonitidae north of Mexico number approxi- 

 mately 135 species and races divided among about 15 genera. 

 Of these, 20 species and varieties, divided among 8 genera, occur 

 in Illinois. Most of the species are restricted to North America 

 but several, among which are Euconulus fulvus and Zonitoides 

 nitidus, are found on three continents. 



Perhaps no group of American land snails has changed so 

 much in nomenclature during the past 15 years as have the 

 Zonitidae. The student of a decade or more ago would scarcely 

 know the species under the generic names now accepted. These 

 changes have been made necessary by the anatomical studies 

 of such zoologists as Dr. H. A. Pilsbry and Dr. H. B. Baker. 



These somewhat drastic changes in familiar names of old 

 and well-known species are deplored by some teachers, but the 

 advancement of scientific knowledge has made them necessary. 

 In many cases the changes have been necessary because of errors 



