Some little tidbits of information:
- A total of 85 different authors were published among the 266 titles of the original 1929-41 series, assuming - and it is a dangerous assumption, admittedly - no pseudonyms.
- By far the most popular author was Edgar Wallace, with no fewer than 54 titles to his credit. Also well represented among the Anglo-American contingent were Agatha Christie with 20, Erle Stanley Gardner with 12, Ellery Queen with 11, S S Van Dine with 10 and Rex Stout with nine. (I don't know about the E D'Errico or A. Varaldo, also in the top-ten but more Italian-sounding.)
- One P. Very wrote Le vipere di cristallo (published 1934). Other giallo-film style titles included the Perry Mason series entry Perry Mason e il mistero del gatto grigio (1938) and T. A. Spagnola's La bambola insanguinata (1935).
- Among the later entries is Dorothy L. Sayer's Clouds of Witness (published 1926) as Il gatto dagli occhi verdi (1948 in Italian translation).