128 BUL1MULUS-BOSTRYX. 



the outer lip unexpanded or expanded, columellar lip dilated 

 above. 



Distribution of typical forms, Chili, Peru, adjacent part of Bolivia 

 and Ecuador, the Andean highland and the Pacific slope ; a group 

 of thin-shelled species, part of them doubtfully referable to this 

 genus, extends eastward across Bolivia and Argentina. 



Bostryx, in the enlarged sense herein proposed, forms a compact, 

 readily recognized subgeneric group, well distinguished by the 

 smooth and frequently rather teat-like apex, more or less calcareous 

 texture, and unexpanded or but little expanded lip. It is an equally 

 compact group geographically, being confined to the elevated 

 Andean region of Peru, Bolivia and Chili and its western slope to 

 the Pacific, with some species in Argentina. To the north and 

 northeast other and distinct groups of Bulimulidw completely re- 

 place Bostryx. 



Although the variation of contour is greater within this subgenus 

 than in any other group of Bulimulida>, the series of species is really 

 not markedly discontinuous, as intermediate forms still existing 

 largely bridge the spaces between the several extremes of divergence. 

 The subdivisions used below are, therefore, groups of but slight syste- 

 matic value, and might well be dispensed with were it not that it 

 seems convenient to divide a subgenus so numerous in species. 



Key to sections of Bostryx. 



I. Shell wider than high, with depressed spire and broad, conic 

 umbilicus Platybostryx, p. 129. 



II. Shell higher than wide, the spire elevated. 



a. Umbilicus large and tubular, Ataxus, p. 130. 



aa. Umbilicus small or imperforate. 



b. Dextral ; sutures very deep ; last whorl free from 

 preceding, or only in contact for a short distance 

 at aperture ; whorls somewhat angular, 



Bostryx, p. 133. 



bb. Sinistral ; slender and elongated, Temesa,p. 134. 

 bbb. Dextral ; whorls not angular, nor with a tendency 

 to become free. 



c. Column-shaped, narrow ; whorls 15-20, 



Geoceras, p. 136. 

 cc. Whorls 11 or fewer. 



