172 CHILONOPSIS. 



Distribution : Island of St. Helena. Two species, C. melan- 

 ioides and C. turtoni still exist in exceedingly restricted areas, 

 where the old island flora is in part preserved ; the others are 

 extinct. 



The species are illustrated on Plate 52. 



Chilonopsis was referred to the Ackatina family by Fischer 

 in 1883, but that position was first demonstrated by the 

 writer in 1896, by the examination of the jaw and radula of 

 C. melanioides (Proc. Acad. N. S. Phila. 1896, p. 418, foot- 

 note 9). Dall first associated the small, thin Bulimuloid 

 forms with the large, solid (7. aurisvulpina (nonpareil), a 

 grouping justified by the conchological characters of the 

 species, which however are remarkably varied in contour, 

 texture and sculpture. A similar diversity of contour is 

 already familiar among species of other generic groups. The 

 Peruvian or Lower Californian Bulimuli, the Philippine Heli- 

 costylas, the Eulotas, and many other genera will immedi- 

 ately be recalled in this connection. 



Among continental genera, Chilonopsis is apparently most 

 nearly related to Pseudoglessula, Siibulona, Trichodina and 

 their allies. All of them have a more or less truncate colu- 

 mella, crenate suture and in the less specialized species, a long, 

 turrited shape. In some forms the sutural crenation has 

 been outgrown and the general shape changed ; but as a whole 

 they are more primitive than the genera of large African 

 Achatinidcz. The common ancestors of all these groups date 

 back to or nearly to the time preceding the Atlantic when 

 Africa and South America were united and supported a com- 

 mon Cretaceous fauna of Achatinidce, Streptaxida, Megas- 

 pirida, etc. and fresh- water mollusks; but there is, so far as 

 I know, no trace of an exclusively South American faunal 

 element in the St. Helena biota. 



CHARACTERISTICS OF THE ST. HELENA SNAIL-FAUNA. Dall 

 has drawn a parallel between the St. Helena and the Gala- 

 pagos snail faunas, tracing their peculiarities of shell sculp- 

 ture and texture to the influence of an environment subject 

 to long arid periods. It is doubtful whether this theory is 

 borne out by the facts. St. Helena was densely forested when 



