Family Discidae
Order Stylommatophora

The angular disk is a heavily-ridged snail shaped like a tiny discus. Mature animals have four whorls at approximately 5mm in diameter (Pilsbry, 1948), and are light brown above, becoming paler below the “bluntly angular” periphery. The umbilicus is open and relatively wide, perhaps more than half the shell width. Its lip is thin. The animal is gray, very dark above.

The angular disk is flatter and more angular than its cousin Discus cronkheiti, a wetland species. Immature angular disks can be distinguished from a smaller relative, Discus patulus, by their lighter color (not dark or reddish), and by their more rapidly-expanding whorls. Small D. patulus may appear more sharply angular than D. catskillensis, though they will become less so in their final whorl.