46 LAURIA. 



angular lamella continued inward as a short or long thread, 

 and a very small columellar lamella, sometimes not reaching 

 to the columella. No palatal folds. 



Viviparous. 



Distribution : Europe, the Atlantic Islands, Africa, Island 

 of Bourbon. 



This group of L. cylindracea is remarkable for its conserva- 

 tism in characters and the wide distribution. Its presence in 

 the Azores, St. Helena and Jamaica is apparently traceable 

 to importation by commerce ; but there are species apparently 

 endemic in places as remote as Madeira, the Canaries, South 

 Africa and Bourbon. None of these vary much from the 

 genotype. 



A few forms are toothless, such as L. sempronii dilucida, 

 and mutations of some forms which normally are toothed. 



Specimens of all of the species except L. vulcanica, L. fagoti 

 and L. desiderata are in the collection of the Academy, most 

 of them in considerable series. 



Key to species of Lauria proper. 



r Palaearctic species, Europe, Atlantic Islands, northern 

 ! ) Africa (2) 



(. Ethiopian species, Abyssinia to the Cape; Bourbon (10) 



Larger species, the diam. (above aperture) 1.5 to 2 mm.; 



base distinctly compressed and subangular (3) 

 Smaller species, thin, diam. 1.2 to 1.6 mm. ; base rounded 

 I or but little compressed (4) 



Umbilicus funnel-shaped, bounded by a strong basal 

 keel. L. umbilicus, no. 2 



Umbilicus moderate, basal keel less pronounced. 



L. cylindracea, no. 1 



r Aperture without teeth of any kind. 



-j L. sempronii dilucida, no. 4a 



(. An angular lamella present (5) 



r A low columellar lamella, sometimes nearly immersed (6) 

 { No columellar lamella in the adult stage (8) 



2 



I 



