ENDODONTIDAE 



87 



DISCUS PATULUS (Deshayes) 



The shell of Discus patulus is similar to that of Discus 

 cronkhitei anthonyi. However, patulus has 6 rather than 4 

 whorls and a wider umbilicus. The brown shell is larger than 

 that of cronkhitei anthonyi, measuring 

 about five-sixteenths inch (8 mm.) in 

 diameter. Its height is less than half 

 its diameter. The surface of the shell 

 is ribbed as in cronkhitei anthonyi. 



Discus patulus is peculiar in having 

 a small white denticle or ridge on the 

 columella located within the aperture. 

 The whole base of the shell in this 

 region is thickened by the presence of 

 this callosity. 



The distribution of patulus in Illi- 

 nois is different from that of cronk- 

 hitei anthonyi. It appears to be most 



abundant in the southern part of the state. The northern 

 ranges, as far as known, are Rock Island, Fulton and Vermilion 

 counties. The habitat of this species is woodlands and wooded 

 valleys of oak, elm, hickory, sycamore and sometimes pine. It 

 is most abundant in rotting logs where the bark has started 

 enough to be loose but is still attached to the old log. In such 

 places, specimens of patulus may often be found by the dozen 

 attached to the rotting wood or to the loose bark. It has been 

 found on floodplains, ravine hillsides, limestone cliffs and in 

 isolated woodlands. 



Discus patulus is not so widely distributed throughout 

 North America as is Discus cronkhitei anthonyi. It is known 

 from Minnesota south to Texas but does not live in Canada or 

 New England and the Middle Atlantic states. Discus patulus 

 is such a characteristic snail that no races have been discovered. 



This snail was previously known as perspectiva, an appro- 

 priate name given by Thomas Say more than a hundred years 

 ago. In older American works on natural history it is listed as 

 Pyramidula perspectiva (Say) or Helix perspectiva Say. But it 

 was found that the name perspectiva had been used at an earlier 

 date for another snail of the same genus, and it became neces- 

 sary to use Deshayes' later name, patulus. 



