EXPLANATION OF THE PLATE. 



The accompanying figure of the UNIO VERRUCOSA OF 

 RAF. (described page 37) is intended to illustrate the fol- 

 lowing parts of the Unio: From A to D the dorsal or 

 hinge margin, which comprises the beaks or apices, as 

 well as the ligament; D to B the anterior margin; A to 

 C the posterior margin ; and C to B the basal margin. 

 The right valve is represented. 



