THE ROCK OYSTERS FAMILY CHAMIDAE. Shellthick, roundish, irregular; valves unequal, ornamented with spines, scales or laminae; beaks sub-spiral; hinge formed by a tooth fitting into a pit; ligament external; mantle closed, gills four, unequal; foot small; siphon small. Large part of family now extinct.
Genus CHAMA, Linn.
Characters of the family. Fifty species, attached to coral reefs in tropical seas. Depth fifty to a hundred fathoms. A few species found elsewhere. Forty fossil species in Cretaceous strata, Europe and United States.
The rock oysters cost all they are worth as an article of diet, for they grow fast to the natural masonry the coral polyp builds, wedged in crevices or attached to stones and shell masses on the ocean floor at considerable depths. They seem to choose most uncomfortable crannies, with no room to gtow, and passively allow themselves to be walled in and smothered. Cramped by their habitation, their spines ground down by movable shells, often overgrown with seaweed and encrusted with sediment, all claims to beauty must be abandoned. Yet where they grow in favouring environment some rock oysters have high colouring and elaborate ornamentation of spines. Their parasitic habit costs them a high price.
The Leafy Chama (C. Lazarus, Linn ) has broad, frond like spines marking the lines of growth on its shells. It is white, tinted with rose. Each frond is delicately striated. This is found frequently in a perfect state. There is no handsomer Chama. Length, 2 to 3 inches.
Habitat.— Mauritius, Philippines.
The Little Archer Chama (C. arcinella, Linn.) is a cool water species, which, when it has a chance, develops a fine array of recurved spines. It is frequently attached to shells of the 36! The Rock Oysters fighting conch (Strambus pugilis). The area about the bases of the spines is peculiarly pitted. Yellowish or white, stained with pink. Lining usually orange. When grown together in a bunch these mollusks modify or lose their spinous ornamentation.
Length, 2 inches.
Habitat.—North Carolina to West Indies.
The Large-leaved Chama (C. macrophylla, Chemn.) has a yellowish shell lined with white. Irregularly distributed are broad lamellar plates, like shingles, on both round valves. Pink and violet specimens are found. The edges of the lamellar are crimped minutely. This species lives a moderately free life. Length, i to 21 inches.
Habitat.—Tampa to West Indies.
The Frondose Chama (C. frondosa, Brod.) spreads over its purple surface a series of broad, fan-shaped lamina', plaited and imbricated, not too closely nor irregularly, producing an effect of unusual richness. The colour is often brightened by yellow. This is one of the largest and handsomest species. Length, 2 to 3 inches.
Habitat.— Western Central America, Gulf of California.
The Pretty Chama (C. pulchella, Rye.) daintily ruffled, snow white, rayed with brown, and very compact of build, shows a peculiarity of the genus. There are rights and lefts, specimens showing opposite directions taken by the spiral beaks. This is a variation due to conditions of growth. Length, r to 2 inches.
Habitat.— New Holland.
The Agate Chama (C. pellucida, Sby.) has its rough exterior adorned by translucent frills, like rose agate or chalcedony. They grow fast to rocks or other submerged objects. You may find the upper valves on the beach. The china-white interior will show a daintily crenulated pallial border. Length, 2 inches.
Habitat.— Southern California.
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