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ed and remains free, never adhering by any part of the 

 valves themselves. The hinge has two curved teeth 

 on the larger valve, inserted and locked into corre- 

 sponding cavities in the smaller. The valves are in 

 some species smooth, in others angular; and some have 

 plaits, which close perfectly, giving the margins a flex- 

 uous appearance. M. de Valenciennes is of opinion, 

 that, where the aperture is not round, and only a notch 

 is observable, it is occasioned by the absence of two 

 small accessory valves or pieces, which seem to com- 

 plete the opening, and which frequently escape notice. 

 The writer considers the larger and perforated valve 

 the upper one, having seen two examples of this shell 

 attached to marine bodies by its pedicle, in both of 

 which the smaller valve was beneath. The animal in 

 its structure very much resembles that of the Lingula, 

 being able, like it, to extend beyond the shell two long 

 posite arms, fringed or ciliated on one side, which, 

 when the animal is at rest, are folded up in a dou- 

 ble plait, with their extremities only curved, or roll- 

 ed iii a spiral form within the shell; the osseous parts, 

 which remain attached to the lesser valve of the Tere- 

 bratula, after the removal of the animal, are called by 

 English collectors the springs of the shell, the pre- 



