The animal on the cover of Mathematica Cookbook is a solarium (genus Solarium) known more commonly today as a sundial or perspective shell. It serves as protection for marine snails of the genus Architectonica (a Latin name which modern scientists also use to refer to the shells). While usually found in the tropical Indo-Pacific region, the solariums also live in warmer waters near North and South America. As the snails prefer shallow habitat, their shells often wash ashore and are an easy find for beachgoers.
There are approximately 40 species, and while texture, coloration, and markings vary accordingly, all solariums have a spiral pattern. On their flattened circular shells, this radiating effect is evocative of the sun, and likely how the animal got its name. Most solarium decorations are vivid, including such motifs as bold lines, grooves, alternating colors, or blotches. Viewed from below, the shell’s deep interior is lined with corrugations that resemble a winding staircase.
The direction in which a snail’s shell coils, interestingly, is comparable to left- or right-handedness in a human. In their larval stage, Architectonica snails begin to develop soft left-coiling shells. However, when the snail enters its adult stage, the solarium reverses direction and spirals to the right as it grows. The majority of gastropods have dextral (right-facing) shells.
The cover image is from Dover Pictorial Archive. The cover font is Adobe ITC Garamond. The text font is Linotype Birka; ...