You are overlooking this bit from the ICZN: 30.1.4.3. A compound genus-group name ending in -ops is to be treated as masculine, regardless of its derivation or of its treatment by its author.
Ah, thanks. That solves the problem. :-)
Now, *why* the ICZN specifies this I do not now.
Maybe some popular 19th-century dictionary erroneously stated it was masculine, and then so many genus names ending in it had been treated as masculine that changing that would have been too much work? Of course I don't know how old "the esteemed Lidell & Scott" is itself.