The genus Discus is one of the land snail genera with representatives both in Europe and North America. There are several species of Discus in North America and 3 in Europe, including D. rotundatus that has been introduced to many countries, including the U.S.
The snail pictured here, D. patulus, is endemic to the U.S. This specimen, whose shell was 8.5 mm in diameter, came from Garrett Co., Maryland.
Thomas Say described this species as Helix perspectiva in 1817 in one of his first papers on snails (Journal of the Academy of Natural Sciences of Philadelphia, vol. 1, p. 18). However, unbeknown to Say, the specific name perspectiva had already been used for another species. So, the name given to it, Helix patula, by Deshayes in 1830 replaced Say's H. perspectiva.
As Say indicated in his description (above), his specimen(s) had been collected by his friend the French naturalist and painter Charles Alexandre Lesueur (1778-1846). Lesueur lived in the U.S. between 1815 and 1837. He was a member of the Academy of Natural Sciences of Philadelphia and later moved to New Harmony, Indiana with Say and others to participate in Richard Owen's short-lived experimental utopian society. Say's wife Lucy took drawing and painting classes from Lesueur in Philadelphia and New Harmony.
According to Say's biographer Stroud (Thomas Say: new world naturalist. 1992), when Lesueur first came to the U.S. he spoke little English. Say read his papers at the Academy's meetings and prepared them for publication in the Academy's journal. In return, Lesueur helped Say with his French and drew illustrations for his articles.
Previous posts about Say and some of the snails he described:
Say’s snails: Helicodiscus parallelus
Cast from the past: the first American papers on American mollusks
Where were you on the night of 30 August 1820?
Cast from the past: Thomas Say’s male and female pulmonates