242 Dr. J. D. Macdonald on the Typical Value of 



shall now attempt the grouping of all the genera which I have 

 found (in many cases by repeated personal observation) refer- 

 able either to Buccinidse or Muricidse, substantiating my posi- 

 tion by satisfactory proof and reference to the labours of others, 

 furnishing decisive evidence in authentic preparations, figures, 

 and descriptions. 



In order that there should be no possible mistake in the 

 types of the two very distinct forms of dentition to which I 

 refer, I have selected two examples for each, viz. those of 

 Buccinum undatum (PL XYI. fig. 1, odontophore laid flat) and 

 Cassidulus melongena (fig. 2) for Buccinidse, and those of 

 Murex tenuispina (fig. 3) and Concholepas peruviana (fig. 4) 

 for Muricidae. 



BUCCINID^. 



Lingual dentition triserial, the distinctive feature of which 

 is a stout conical fang at the inner extremity of the pleural 

 plates. 



