Done! Just in time to switch over to spring and summer knits. These are very cute and soft, but probably won't get much use until next winter. The pattern is Hippocampus, by Toritot Design, which is free (wee!) and comes in French, English, or Portugese.
I knitted the small size, but used size 1 needles (pattern calls for US 1.5), so they are extra-small. I have extra-small hands and they fit like, er, a glove. I also changed the yarns--the pattern uses two different color-changing yarns (actually, I think the designer took a single color-changing yarn, then cut/pasted all fragments into two balls of the same color family, which seemed pretty ridiculous), but I used a solid black for background, and a slow-changing yarn for the foreground, for a sort of stained-glass effect.
The color-changing yarn is Crystal Palace MiniMochi, and the black is Schachenmayr nomotta Regia 4-ply. (Totally had to copy and paste that second yarn name.) The whole pair used up less than half of each ball. Both are very soft and easy to work with, and the MiniMochi colors change at the perfect rate for this pattern--I went through just over one color repeat over the two pairs.
I followed the pattern exactly, except I striped the cuff to make it more fun. The only beef I have with this pattern, and most glove patterns, is that the thumb is not where the real thumb is. Many glove/mitten patterns with thumb gussets have the thumb too far on the side. Others have afterthought thumbs that are entirely on the palm. This one, although there is a gusset followed by an afterthought thumb, is entirely on the palm. Very strange!
For those who are wondering, hippocampi are indeed brain structures. They are located on the medial surface of the temporal lobes, and play a huge role in memory formation. One of the most famous neurology patients, H.M., had both hippocampi removed when he was young and subsequently could not make new memories. The brain hippocampi (singular = hippocampus) are named for the animal hippocampus (sea horse), because the cell layers curl around each other and look like the tail of a sea horse. (See purple picture at bottom of this page for a demonstration.) A brain hippocampus is not named for hippopotamus or Hippocrates, although those would be fun too! In any case, I think this mitten pattern is quite suitable for a neurologist!