12 GASTROCOPTA, NORTH AMERICA, WEST INDIES. 



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

 plicas unspecialized, the upper and basal small or sometimes 

 wanting; the basal not subcoluniellar 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 



I I 



Sinalbinula 



Privatula 



Limiersidens- 



-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. 



1}. Palatal plica? present. Subgenus Vertigopsis, spe- 

 cies nos. 4 to 7. 

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



species no. 15. 



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

 &. Palatal plicas standing 011 a white callous ; aperture 

 nearly filled by the large teeth. Subgenus Albinula, 

 species nos. 1 to 3. 

 & 1 . Palatal plica? 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. 



