From Barry Roth:

Vespericola was validly proposed on an introductory page (XVII) of volume 1, part 1 of Pilsbry's Land Mollusca of North America (1939). There the new genus-name was not printed attached to any associated species-name. Thus its gender was unspecified. Per the Code, in such cases the gender is to be treated as masculine. The fact that Pilsbry treated it as feminine in his full (1940) writeup is irrelevant.

https://www.inaturalist.org/observations/86789471
https://www.inaturalist.org/flags/518823