VERMETID^E. 165 



b. Shell wiih. interior plications or lamellae. 



3. Genus YERMETUS, Adanson. 



With a single columellar plication. S. G. YERMETUS. 

 With parietal lamellae. S. G. PETALOCONCHUS. 



Synopsis of Genera. 



Genus YERMETUS, Adanson, 1757. 



Animal having two pedal filaments, much longer than and 

 situated in front and below the cephalic tentacles. 



Shell tubular, free or fixed, sometimes regularly spiral when 

 young, but becoming irregularly protracted or contorted when 

 adult, with interior septa; aperture circular ; operculum usually 

 present, corneous, annular, circular, exteriorly concave. 



Inhabits temperate and tropical seas. Fossil, secondary and 

 tertiary. 



Subgenus YERMETUS (sensu stricto). 



Shell spirally twisted, attached, surface often decussated, 

 columella bearing one to three longitudinal lamellae. Operculum 

 very small, concave, scarcely spiral. 



Section YERMETUS (typical). 



Laminae on the parietal wall. 

 Section PETALOCONCHUS, Lea, 1843. 



Shell with two internal ridges running spirally along the colu- 

 mella, becoming obsolete towards the apex and aperture. Mostly 

 fossil. 



Y. SCULPTURATUS, Lea. Tertiary. U. S. (S. and S. Conch., t, 67, 

 f. 76). 



Section MACROPHRAGMA, Carp., 1857. 



Internal laminae towards the middle of the columella ; superior 

 lamina sharp, angulately deflexed, externally bicarinate. 



Operculum small, very thin, corneous, smooth, subplanate, 

 scarcely spiral. 



Section ALETES, Carpenter, 1857. 



Whorls larger than in preceding section, columella with a very 



