One Fish Two Fish Red Fish Blue Fish (1960 Edition)

Source: http://www.amazon.com.Dr. Seuss Enterprises, L.P. License: All Rights Reserved.

Most of Dr. Seuss's books had only his hand lettering on the cover, but this title uses a font. The letters appear to match Cambra on page 18 of the "Alphabet Thesaurus, Vol. 2" published by Photo-Lettering, Inc. New Century Schoolbook was used for the interior of this and many of the other first edition Dr. Seuss books.

Update:Stuart Sandler informs me that this is actually Filmotype Major, released as a photocompositor font in 1951. It was recently revived by Rian Hughes and released under the new digital incarnation of the Filmotype foundry owned by Sandler.

Update Jan 19, 2016: Steve Jackaman of International TypeFounders adds

We produced several new Dr. Seuss fonts in digital form about 20 years ago, based on just a few glyphs from their multiple logo styles and early examples.

Dr. Seuss editions after 1995 may use these ITF fonts.

Source: http://www.amazon.com.Dr. Seuss Enterprises, L.P. License: All Rights Reserved.

Source: http://geekosity.blogspot.com.Dr. Seuss Enterprises, L.P. License: All Rights Reserved.