I find these every winter at night during/after rain. They are very active and hardly at all afraid of light or touch (which makes them rather hard to photograph). I have never found mature adults, but there appears to be a substantial population: tonight I found 13 individuals varying from 9 to 20 mm wide after it had been raining for 7.5 hours. They live in a developed area along the creek, cohabiting with Xerotricha conspurcata and Cornu aspersum (and possibly Oxychilus draparnaudi). They appear to live under the rocks, most if not all of which were put there by people.

This individual:
Whorls: 5 1/4
Width: 16.9 mm
Height: 11.6 mm
Umbilical width: 1.9 mm
Band width: 1.3 mm
Aperture width: 10.0 mm
Eye stalk length: 9.6 mm
Tentacle length: 2.7 mm
Foot width: 7.5 mm
Longest dimension when stretched all the way out: 47 mm