"Oh, a great deal of difference," declared Nan, wagging her head wisely;
"a kelpie is an imaginary water sprite, you know, and a pixy is a--a--
why, a sort of make-believe fairy who lives in the water."

"Well, I'm glad that you see a difference in your two definitions. For
my part I don't see anything to hinder my being a kelpie and a pixy
both, even if I'm not twins."

"Well, they're not so very different, you know. One is a kelpie, and one
is a pixy; that's about all the difference."

Patty laughed. "Well, if it will help you out any to have me make a
choice," she said, "I'll choose to be a kelpie. What's the latest thing
in kelpie costumes?"

"Oh, it will be lovely, Patty! I'll have it made of pale green silk,
with a frosted, silvery, shimmering effect, you know, and draped with
trailing green seaweed and water grasses."

"Lovely!" agreed Patty. "And what would the pixy costume have been, if I
had chosen that?"

"Just the same," confessed Nan, laughing; "but it's easier to have
something definite to work at. You can wear my corals, Patty, and, with
your hair down, you'll be a perfect kelpie."

Patty smiled at her young stepmother's enthusiasm, and Nan ran away to
begin preparations for the kelpie costume.

The night of the party the whole Fairfield house was so transformed that