SUCCINEIDAE 



125 



SUCCINEA RETUSA Lea 



Unlike most Succinea snails, two species, retusa and salleana, 

 are inhabitants of wet and marshy places, living on partly sub- 

 merged sticks, on water plants, such as cattails, or on wet mud 

 near the margins of streams. 



The shell of Succinea retusa, usually 

 bright amber in color, has a short spire and 

 a very large and long aperture. Succinea 

 concordialis is the only Illinois species which 

 might be confused with retusa, but con- 

 cordialis usually has a wider shell, and its 

 aperture is obliquely ovate. 



The animals of Succinea retusa vary in 

 color from yellowish to black, and are more 

 or less mottled or spotted. A curious change 

 in color coincident with the season has been 

 observed in this species, for the animal is 

 dark colored or black in the spring and is 

 of the same amber color as the shell in late summer and autumn. 



Like many other Illinois land snails, retusa varies consider- 

 ably in form, and several varieties have been named. 



Succinea retusa retusa Lea. Fig. A. The shell of the typical 

 form is about five-eighths to three-fourths inch (16-20 mm.) in 

 height. It is very fragile, the shell substance being thin. The 

 spire is short and pointed. The aperture, which is narrow and 

 acutely angled above, is long and wide below. It extends about 

 two-thirds the length of the entire shell. The edge of the lip 

 is sharp and thin. The shell has 3 whorls, the first 2 small, 

 the last or body whorl large and elongated. The columellar 

 region is arched, and the parietal wall usually has a light wash 

 of callus. 



Found in various parts of the state. Succinea retusa retusa 

 has been reported more often from the northern than from the 

 southern half. 



Succinea retusa magister Pilsbry. Fig. B. The variety retusa 

 magister has a shell which measures about three-fourths inch 

 (18-20 mm.) in height. It is slightly longer than that of retusa 

 retusa. The spire is usually shorter and wider than in the 

 typical form, and the aperture longer and wider. The color 

 is usually lighter than that of retusa retusa, often grayish. At 



