VITRINELLA ADAMS. 



Testa turbiniformi, minima, vitrea ; apertura maxima, orbicular!, 

 subtus valde indentata, vel umbilicata. 



Shell turbiniform, vitreous, minute, with a large orbicular 

 aperture, either umbilicated or with the umbilical region deeply 

 and widely indented. 



The form of the aperture would place these shells in Turbo 

 or Margarita. The want of an umbilicus excludes three of 

 tlic species from the latter. The operculum is unknown ; but 

 as it is extremely improbable that thin vitreous almost transpa- 

 rent shells should have solid calcareous opcrcula, we may as- 

 sume it to be horny, which will exclude the species from Tur- 

 bo, regarding this genus as best characterized by the opercu- 

 lum. The most widely umbilicated species approximates in form 

 to Skenca, and might be mistaken for a depressed umbilicated 

 species of Helix. In texture, the nearest approach among the 

 kindred genera is in Margarita arctica Leach. From all the 

 Turbinida3 known to us, they are liowevcr well distinguished by 

 their vitreous texture and rapid enlargement of the whorls, 

 which last character produces a large aperture. The variation 



