However, this is a Kempo blog, not a Shotokan blog, so bringing things back to the topic at hand, is the short passage on Okinawan Kempo on page 136.
"For the record, we also see a fourth kind of karate in Japan and Okinawa, usually labeled kempo. "Kenpo" is the Japanese pronunciation of the Chinese "chuan fa' kanji. Kenpo is originally kung fu in a Japanese uniform, but in recent years it has mixed in liberal amounts of other martial arts."
This quote was in a section on the three main, distinct schools of Okinawan Karate (Naha-te, Shuri-te and the arts based on ChotokuKyan).
Personally, I like Dr. Clayton's description of Kempo, even though he gives in a fairly dismissive and offhand matter. It does actually describe the early history of Kempo in the United States, and in particular, the martial arts melting pot of Hawaii in the 1950s and 1960s.