Published September 20, 1888, according to Marshall B. A. (1991)
The Nautilus, 105 (3): 104-115. This is a reprint published in advance of
Memorie della Reale Accademia di Torino, (2) 39 (June 1, 1889) with identical contents but distinct pagination.
Published January 15, 1887, according to Marshall B. A. (1991)
The Nautilus, 105 (3): 104-115. This is a reprint published in advance of
Memorie della Reale Accademia di Torino, (2) 38: 79-166 (March 1, 1888) with identical contents but distinct pagination