The Thorny Oysters 



sometimes two or three inches thick, have their dense cover of 

 flat spines entirely overlaid with a chalky lime deposit. Only a 

 remnant of colour, orange or purple, remains tinging the fluted 

 lips inside, and the beak. Wide ruffles extend out from the sides 

 of some specimens. The white lining is china-like, with deep 

 muscle scars. 



The peculiarity of the attached valve is that it contains water 

 chambers, flat, extensive, between the layers of the growing shell. 

 The border of the mantle deposits material faster than the hinge 

 area, in early stages the upper valve is bright rose colour, with 

 three narrow dark ridges. Subsequent growth is colourless. 

 Length, 5 to 6 inches. 



Habitat. — Pacific Islands. 



The Lime-Carrier (S. calcifer, Cpr.), with ruby lips, has its 

 orange-coloured spiny face quite buried under burdensome depos- 

 its of lime. This species seems much like its predecessor, but is 

 more compactly built. Diameter, 5 to 8 inches. 



Habitat. — Panama to California. 



The American Thorny Oyster (S. Americanus, Lam.) 

 varies in its shape and the character of its spines. The scallop- 

 like, eared valves are whitish or brightly painted with yellow, 

 and shades of red. The valves are ribbed, the area sub-divided 

 by six extra ribs of greater size. The spines vary from needles, 

 long and short, to broad, laminate frills, irregularly formed and 

 distributed on a given specimen. The texture throughout these 

 forms is china-like. Length, 3 to 6 inches. 



Habitat. — Bermuda, West Indies. 



The Imperial Thorny Oyster (5. imperialis, Chemn.), 

 one of the most beautiful of its tribe, is fortunately abundant, 

 and quite common in collections. Its valves are similar, round 

 and eared like a scallop shell. Six main ridges separate the low 

 ribs into groups of threes. Sharp spines, a single row on each 

 ridge, cover the surface. The short ones on the secondary ridges 

 are re-curved and each has a basal pair of minute points. The 

 long primary spines overlap each other. This species never 

 attaches itself, but remains free through life. The rosy flesh tint 

 of these elegant shells deepens between the ridges. Diameter, 

 2 to 3 inches. 



Habitat. — China. 



The Royal Thorny Oyster (S. regius, Linn.) larger, mo-'e 



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