Pseudodoxia V.7 . Known to be a forgery even in Ross's day. The general consensus is that it was written early in the 13th century, probably for the use to which Ross puts it. Most convincingly, in Pseudodoxia V.8 . Pseudodoxia V.9 .
Ancient etymologies are frequently wrong, often fantastically so.
They do, however, give some sense of the meanings of the words to which they are attached. XXI, does not not specify the number of serpents. Iliad 184 ff. If you ask me, making a speech to a horse is a sure sign that one is not familiar with the beasts. It is difficult to know what, if anything, Ross was thinking when he wrote this little passage.