= ibs} s 
The Stylommatophora are divided into four suborders, the Orthurethra, 
Mesurethra, Heterurethra, and Sigmurethra, on the basis of the internal 
structure and arrangement of the kidney and ureter. The Sigmurethran 
group is the most advanced and by far the most important withthe greatest 
number of species (and the only one considered inthis publication). It 
differs from the others inthat the ureteris abruptly reflexed from the apex 
of the kidney and passes to the posterior end of the lung cavity. It then 
follows the digestive tract anteriorly to the mantle edge. This sigmoid form 
of ureter is not found in the other three suborders, 
The sigmurethran snails fall into two divisions according to the position of 
the pedal grooves of the foot. The pedal grooves are found at the boundaries 
where the tuberculate side walls of the foot join the smoothventral sole. In 
the Holopoda, such as Helix, Cepaea, Otala, Lamellaxis and Testacella, 
the pedal grooves are inconspicuous and in or close to the angle of the 
lateral margins of the foot. In the Aulacopoda, for example, Oxychilus, 
Limax, Deroceras, Milax, and Arion, it is situated higher so that part of 
the sole actually comes around to form part of the more or less vertical 
side of the foot. In snails or slugs of this latter group there is a second 
rather weakly impressed groove above and running parallel to the pedal 
groove, the suprapedal groove (see fig. 7). 
