The organizing principle of this unusual counting book is the mathematical Fibonacci sequence (1, 1, 2, 3, 5, 8, 13, etc.), which, when plotted on a graph, forms an “equiangular spiral”—a curve frequently found in nature. Thus, one animal with a Fibonacci spiral (walrus tusk) leads to another (elephant tusk), accumulating according to the pattern. Two parrots’ beaks, three crocodiles’ teeth and five raptors’ talons progress to 55 ibises’ bills and 89 spiraled seashells. Schwartz’s finely detailed illustrations depict the easily counted animals in their habitats, panels at the leading edge of each spread featuring dots and equations that illustrate where readers are in the sequence. Hulme’s simplistic verse is disappointingly out of sync with the complexity of the mathematical and zoological concepts here, however; the reader must sludge through a densely packed double-page spread of explanation before launching into the main narrative in order to begin to grasp what is going on. Older readers will rankle at the delivery, and younger readers will miss the point completely. It’s an entirely novel way to present a very tricky idea, but it just doesn’t add up quite right. *(Picture book. 7+)*