The Hippopotamus.

"OH, say, what is this fearful, wild
In-cor-ri-gible cuss?"
"This crea-ture (don't say 'cuss,' my child;
'T is slang) - this crea-ture fierce is styled The Hip-po-pot-am-us.
His curious name de-rives its source
From two Greek words: hippos - a horse,
Potamos - river.    See?
The river's plain e-nough, of course;
But why they called that thing a horse,
That's what is Greek to me."