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ty-one species, all of which possess some precisely defin- 

 ed difference of character, though many of them are but 

 very slightly indicated. The S. regius is considered a ve- 

 ry rare species, and has been ably described and figured 

 in Sowerby's Genera of Shells. The shells of this genus 

 are inequivalve, adhesive, attaching themselves to each 

 other, or to stones, corals, and other marine bodies; 

 summits unequal, the lower valve exhibiting a more or 

 less long, flat, internal slope, divided by a groove, in 

 which a portion of the ligament is inserted, becoming 

 enlarged by age: valves eared, and their exterior 

 ribbed, and armed with long recurved, or nearly 

 straight spines, terminated in a point, or palmated. 

 On the lower valve, which is always the largest, 

 there are broad foliaceous laminae, by which the 

 shell is affixed to other substances; apices unequal, 

 distant, and recurved inwards ; margin of the valves 

 smooth or crenulated, and closely shutting. Hinge 

 with two strong hooked teeth on each valve articulat- 

 ing together, an intermediate cavity for the ligament, 

 communicating at the base with the external groove 

 in the summit of the lower valve, ligament interior, 

 and a portion of it seen externally in the lower chan- 

 nel. They possess no locomotive power. 



