OF CONCHOLOGY. 23 



the present group, rather than with Cerithium. The manner of 

 junction posteriorly, between the outer and inner lip, and the 

 form of the latter are only exao;gerations of what occurs in 

 Anchura. (See for example A. Mexieana, nob.) From Piette's 

 figures, by which alone I know the genus, it appears to be an 

 Anchura, deprived of its expanded outer lip, and with the stump 

 thickened. 



There is yet much to be done before we shall have arrived at 

 a full understanding of the alate and digitate shells of the sec- 

 ondary rocks ; but until we shall have become better acquainted 

 with some of the numerous species, as yet only known from 

 fragments, the final classification of the genera must remain 

 an open and perhaps a disputed question. If I have thrown 

 any light on it, or if I only succeed in attracting the attention 

 of other students to the subject, I shall be perfectly content. 



