Location: School of Fish
Depth: 377

Solution to The Wheels Go Round and Round

by Noam D. Elkies

Answer: SEDAN

Solution to the clues:

CH2O solution used as a preservative  FORMALIN
“Northern” fish PIKE
“Psst!” LISTEN
Slippery to the max EELIEST
Twenty-third of twenty-four PSI
Valse ou rigaudon DANSE
Barely wet one’s whistle SIP
Gendarme’s ceremonial cap KEPI
Metallic playing marble STEELIE
Not burdened by stiff ceremony INFORMAL
Sign on ENLIST

Each word in the top, except for DANSE, can be tranformed to get a word on the bottom by moving two letters from the end to the beginning. (For example, FORMALIN becomes INFORMAL.) If we apply this transformation to the leftover word DANSE, we get SEDAN, which is the answer.