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THE AMERICAN NATURALIST [Vol. XLIII 



ventromediaii is well preserved posteriorly, but its an- 

 terior portion has been broken away. The impression 

 of this missing part is, however, well preserved on the 

 surface of the matrix and there is no difficulty in restor- 

 ing the outline of this plate on its forward margin. 

 Posteriorly it meets the postero-ventromedian, the limits 



of the two plates being indicated by a curved line whose 

 convex side is directed forward. The postero-ventro- 

 median is clearly outlined, though its surface has been 

 considerably crushed. The antero-ventrolaterals border 

 the two median plates on either side. It is impossible 



