From The World of Nabokov’s Stories (1999), by Maxim D. Shrayer:
In an 1971 interview with Stephen Jan Parker, Nabokov said: “In relation to the typical novel the short story represents a small Alpine, or Polar, form. It looks different, but is conspecific with the novel and is linked to it by intermediate clines.” Critics have inquired into the meaning of Nabokov’s statement and the light it sheds upon the study of his short stories. By “conspecificity,” I believe, Nabokov meant most of all that his “short stories are produced in exactly the same way as [his] novels and informed by their [a]uthor and his subtexts [italics added].” Nabokov’s working and somewhat tentative definition, based primarily on the criterion of textual length, lacks a second criterion related to the structure of composition. When working on his “small Alpine forms,” I experienced a need to draw a line between the short stories and the transitional or hybrid forms. The latter include two short novels, Sogliadatai (The Eye, 1930) and Volshebnik (The Enchanter, 1939, published 1986) and two chapters of an abandoned novel (”Solus Rex,” 1940, and “Ultima Thule,” 1942) which appeared in periodicals and collections in the guise of separate short fictions. I have decided to exclude them from my analysis. At the same time, I could not leave several of the early plotless fictions out of my study. Virtually eventless, “Groza” (The Thunderstorm, 1924) satisfies the criterion of length, but not of structure, as I have conceived of it in this study. A few, like the very early “Nezhit”‘ (The Woodsprite, 1921) or “Slovo” (The Word, 1923), correspond to the genre of creative nonfiction. Finally, there is also the exhilarating case of “A Guide to Berlin,” which is not a short story but a sequence of five vignettes of the type that Ernest Hemingway inserted between his short stories in the collection In Our Time (1925).
(Hat tip to Chris Power’s “A brief survey of the short story part 28: Vladimir Nabokov.”)