12 GASTROCOPTA, NORTH AMERICA, WEST INDIES. 



horizontal, or with a callous below the inner end. Palatal 

 plicae unspecialized, the upper and basal small or sometimes 

 wanting; the basal not subcolumellar in position. Type G. 

 acarus (species 16 to 33, 66 to 78, 86, 87). 



The interrelations of the subgenera, so far as now under- 

 stood, may be roughly indicated by a diagram: 



Albinula 



Australbinula Vertigopsis 



Sinalbinula 



I 



Immersidens- 



Privatula 



Gastrooopta 



I. NORTH AMERICAN AND WEST INDIAN SPECIES. 

 Temperate North America has by far the most diversified 

 Gastrocopta fauna of any continent, five subgenera being 

 represented. Three of these, Albinula, Vertigopsis and Pri- 

 vatula, are notable for their specialization and the small 

 number of species. 



Key to Subgenera. 

 a. Teeth of the parietal wall small or minute. 



&. Palatal plicae present. Subgenus Vertigopsis, spe- 

 cies nos. 4 to 7. 

 6 1 . No palatal plicae or callous. Subgenus Privatula, 



species no. 15. 



e 1 . Teeth of the parietal wall moderately or well developed. 

 b. Palatal plicae standing on a white callous; aperture 

 nearly filled by the large teeth. Subgenus Albinula, 

 species nos. 1 to 3. 

 6 1 . Palatal plicae not joined by a callous. 



c. Angular and parietal lamellae diverging for- 

 ward, the whole like a reversed (mirrored) 

 letter "y". Subgenus Immersidens, species 

 nos. 8 to 14. 



c 1 . Angular and parietal wholly concrescent into 

 a sinuous lamella, or with the parietal pro- 

 jecting very little forward. Subgenus Gas- 

 trocopta, species nos. 16 to 25. 



