I like novels about cryptozoological subjects, and my friend Loren Coleman sent me this one a few years ago. I'd overlooked it until now.
Corey's Sea Monster
by Rutherford G. Montgomery, World Publishing Company.
This 1969 novel for young readers is the only time I've ever seen the dunkleosteus used in a novel, except for a brief appearance in one of Steve Alten's books. While the marine biology is here is pretty sketchy even for 1969 (who knew it was easy to photograph a giant squid underwater? And what IS an electric eel doing in the Pacific?) it's fun. Interestingly, the author uses the name of the related species Dinichthys, but the illustrations are clearly meant to be Dunkleosteus terrelli. Mr. Montgomery makes the modern version a pelagic (open ocean) fish that in one casem for reasons unknown, decides to hang out in a sea cave off California. He also makes it glow all over with bioluminescence. (Did Mr. Alten perhaps read this befpre he came up with his glowing Megamouth shark?)
Modern teenagers will consider the book too tame, and divers will blanch at the way the young hero's father routinely sends him on deep dives alone to photograph dangerous animals, but it's a harmless diversion, and it was certainly an original storyline for its day.