174 HYPSELOSTOMA-BOYSIDIA GROUP. 



proper to their group. It is this interlacing of characters 

 which has influenced me to retain Boysidia and Paraboysidia 

 in one genus. Eventually I believe that the two will be sep- 

 arated ; but no doubt a great many species remain to be dis- 

 covered in southern China and Indo-China, and they will test 

 the distinctions now drawn. 



The diagnostic characters of the genera and subgenera are 

 given below in the form of a key, in which entries are also 

 made for the determination of aberrant species. 



Key to Genera and Subgenera. 



a. Angular and parietal lamellae concrescent into one sin- 

 uous or lobed lamella. 



b. Last whorl adnate to the preceding. 



c. Columellar lamella descending steeply inward. 



BOYSIDIA. 



c 1 . Entering part of columellar lamella hori- 

 zontal; peristome interrupted above, Boysidia 

 robusta. 



b l . Last whorl becoming free, projecting or ascending. 



HYPSELOSTOMA. 



a 1 . Angular and parietal lamellae distinct and parallel. 

 b. Last whorl adnate to the preceding. 



c. Columellar lamella horizontally entering. 

 d. Teeth ending outwardly in hooks. 



BENSONELLA. 



d 1 . Teeth simple, not hooked. PARABOYSIDIA. 

 c 1 . Columellar lamella descending inward, Boy- 

 sidia strophostoma. 

 b 1 . Last whorl becoming free and projecting. 



GYLIAUCHEN. 

 a 2 . No angular lamella, the parietal standing alone ; last whorl 



adnate to the preceding ANAUCHEN. 



a 3 . No teeth in the aperture; last whorl becoming free in 

 front, Hypselostoma edentulum. 



