This snail is Zonitoides nitidus, common name Black Gloss. I found truckloads of these individuals at Kirby Park. According to Pilsbry:
This species is common and generally distributed in the Canadian Zone, more local, though abundant when found, in the Northern part of the Alleghanian fauna, Transition Zone... Z. nitidus is generally found near water or in marshy places, never in upland woods where Z. arboreus lives. In late autumn they sometimes occur in great numbers under dead wood in wet places, where they have assembled for hibernation.
That generally describes my area here in Northeastern Pennsylvania and where I found them: in the Susquehanna River floodplain. Also when I found these individuals-- late September through October.
The animal is a dark blue-gray and has pinkish flecks, most abundant on its sole, less so elsewhere. Another interesting characteristic is that through the shell- near the aperture- you can see an orange-ish organ which I thought to be maybe a heart, but apparently is a lung. This must be what Pilsbry means by "Lung: aerating surface deeply pigmented." Click on the photo to enlarge and see what I mean.
This snail, like its close relative Z. arboreus, is in the family Gastrodontidae, but the genera is named to harken to the family which these snails can resemble, Zonitidae. In fact, at first I believed these snails to be of the introduced genera Oxychilus, mostly because Kirby Park is a former garden which could have easily transported introduced species. In fact, the most abundant land mollusk I've noted in the park is Deroceras reticulum, an introduced slug of the Agriolimidae family.
The measurements of this individual photographed are:
Umbilicus: Umbilicate, 1.2mm, Can see all the way to the last whorl
Shell: Somewhat transparent, about 5 whorls, amber tinted
Body: Dark blue-gray (slate) with pinkish flecks mostly at sole. Eyes are short and stout.
|Range map from Land Snails of Limestone Communities and Update of Land Snail Distributions in Pennsylvania (Pearce)|