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triangular, giving attachment to the biarticulated plates 

 at a single point on its outer margins near the base, which 

 enables the animal to close them together in a line along 

 its centre beneath. These plates are about the length of 

 the segment, and of a triangulate form, each one having 

 near its termination a small oval articulation. The seg- 

 ment and marginal plates are slightly inflated along their 

 external edges, producing an obtusely elevated border. 



The segments constituting the thorax and post-abdomen 

 are supplied by a central, angular, and elongated knob, 

 which, when united, form a prominent dorsal ridge, 

 gradually diminishing in its backward course, and form- 

 ing a sharp elevated line along the caudal segment, ter- 

 minating at its extremity in a short and obtusely pointed 

 spine. 



This beautiful crustacean furnisiies to us another close 

 approximation to the long lost family of the Trilobite. I 

 procured them from the southern shores of the New South 

 Shetland Islands. They inhabit the bottom of the sea, 

 and are only to be obtained when thrown far upon the 

 shores by the immense surges that prevail when the de- 

 tached glaciers from the land precipitate themselves into 

 the ocean. 



