Volva, no ring, Volvaria.
"Among the Mushrooms" by Ellen M. Dallas and Caroline A. Burgin
Genres Volvaria, Ampullaria, Planorbis.
"Lamarck, the Founder of Evolution" by Alpheus Spring Packard
This is the smallest species of the Volvaria.
"The Mushroom, Edible and Otherwise" by M. E. Hard
The volva is a feature of great importance in the study of the Agaricini, of the subgenera Amanita, Volvaria, etc.
"Student's Hand-book of Mushrooms of America, Edible and Poisonous" by Thomas Taylor