384 INTRODUCTION TO CONCHOLOGY. 



Family I. Tendinosa. 



" The minutest throb, 

 That through their frame diffuses 

 The slightest, faintest motion, 

 Is fixed and indispensable." — Shelley. 



Tendinous Brachiopods are divided from tlieir sessile 

 brethren in the same manner as the Lepades : the pedicle of 

 the former, however, differs from the latter both with regard 

 to its use and situation. Instead of supporting the shell, 

 as in the instance above cited, or being used as a kind of 

 nest for the reception of eggs, it serves to afford the animal 

 a limited sphere of motion ; thus causing him to sway gently, 

 like many grasses that grow low upon the ground. Occa- 

 sionally some of this curious tribe become attached by a 

 number of short fibres passing through an orifice in the 

 under valve. They are divided accordingly into two genera, 

 Lingula and Terehratula ; in the former of which the shell 

 is equivalve, in the latter inequivalve. 



In addition to peculiarities of construction or appendages, 

 already mentioned, the shell of the Lingula may be described 

 as being thin, either horny or calcareous, and of a green or 

 somewhat ruddy colour, slightly beaked at the apex, and 



