105 



Mil REX. 



A. Spinous, with a produced beak. (Plate 



XVIII. %. 1.) 



B. Having longitudinal sutures, or varices, ex- 



panding into crisped foliations : beak ab- 

 breviated, (fig. 2.) 



C. With thick protuberant, rounded, sutures; 



varicose, (fig. 3.) 



D. More or less spinous, and without any beak. 



(fig. 4.) 



E. Unarmed with spines, and having a long, 



straight, subulate beak. (fig. 5.) 



F. Tapering, with a long spire and short 



beak. (fig. 6.) 



G. With a toothed columella. (Plate XXIII. 



fig. 2.) 



Shell univalve, spiral, often formed with longi- 

 tudinal membranaceous sutures. Aperture termi- 

 nating in a canal either straight or turned up 

 backwards, and not inclining either to the right 

 or left. 



