48 VARICELLA. 



throughout a considerable portion otf Tertiary time. The 

 wide distribution of the single species V. gracillima is not 

 readily explicable at present. It belongs in a class with nu- 

 merous other minute shells, Opeas, Thysanophora, Pseudo- 

 hyalina, Bifidaria, etc., which have been widely spread by 

 some such unusual means of transport as tornados, which 

 might carry them, together with the dry leaves, etc. among 

 which 'they live, for long distances. 



Of the 75 species of this genus now known, 28 were briefly 

 described and figured by Tryon in vol. I of this work. The 

 small and slender forms were at that time thought to belong 

 to the Stenogyroid group of Achatinidse. In my study of the 

 species omitted from Tryon 's account, I found it necessary 

 to examine the whole series, and to study the types of a large 

 number of them in the Adams collection at Amherst; and it 

 was deemed best to give here the results of my studies upon 

 the species included in vol. I. together with the others, re- 

 stricting the 'account to new matter and figures, essential to 

 the proper identification of the forms, and not duplicating 

 information given in Tryon 's monograph. 



Very little is known of the detailed distribution of the 

 Jamaican species. Prof. C. B. Adams, who personally col- 

 lected many of them, was satisfied to label his specimens 

 " Jamaica," 'and all record of the type localities is lost, ex- 

 cept in a few cases. The few records made by later authors 

 are not always trustworthy, since no adequate means existed 

 for the exact determination of their specimens. I have been 

 enabled to supply data on many species from the collections 

 of Mr. J. B. Henderson of Washington, generously placed 

 at my disposal. 



Key to Subgenera and Sections of Varicella. 



I. Neanic and adult sculpture of spaced ribs with much finer 

 striae in the intervals, and with occasional varices ; some- 

 times also striate spirally. Embryonic shell pupiform 

 or cylindric, of 2% to 3 l / 2 long whorls, vertically striate 

 except the first whorl or half whorl. Columella truncate 

 or almost simple. Shell small and slender. 



Subgenus PICHARDIELLA, p. 50. 



