CHILONOPSIS. 173 



C. aurisvulpina and most of the other species existed, and 

 there is every reason to believe that the snail fauna was wholly 

 unaffected by deficient or irregular water supply. The shells 

 had not the coloration of arid-country snails. C. aurisvulpina 

 is a markedly phylogerontic form, and was probably nearing 

 extinction when the catastrophy was precipitated by the de- 

 foresting of the island. The sculptural peculiarities of the 

 others are easiy paralleled in forms inhabiting notably humid 

 regions such as St. Thome, Cameroons, etc. 



St. Helena exhibits two common characteristics of almost 

 all old island-faunas: (1) a very small number of original 

 generic types, in this case about six, some one or two of 

 which have been greatly modified to fill stations commonly 

 occupied by species of several genera. Cf. Pcecilozonites in 

 Bermuda; Mandarina and Hirasea in the Bonin Is.; Acha- 

 tinellidcc in the Hawaiian group; (2) accelerated aging of 

 the genera so modified, resulting in unusually large forms 

 variously calloused or irregularly coiled, being often unduly 

 elevated or depressed for their genera, stigmata of old age 

 of the group. This results in an unusual proportion of ex- 

 tinct species, especially if the equilibrium of the fauna be in 

 any way disturbed; and the forms which drop out are as a 

 rule, those with phylogerontic characters. Cf. in Bermuda, 

 Pcecilozonites nelsoni, cupula, zonata; in the Bonins, Man- 

 darina ruschenbergeriana, pallasiana; in the Madeiras, Geo- 

 mitra delphinula, bowdichiana, Leptaxis lowei, etc. In New 

 Caledonia the most ponderous and heavily calloused Placos- 

 tyles. The list could be greatly extended. 



It seems therefore that the characteristics of the St. 

 Helena snail fauna are those of an ancient, isolated fauna, 

 rather than traceable to aridity of climate. 



NOMENCLATURE. The name Pachyotus has been used for 

 C. aurisvulpina by most authors, in either a generic or sub- 

 generic sense. That name was proposed by Beck in 1837 for 

 a series of Brazilian forms and the species B. aurisvulpina, 

 no type being selected. Herrmannsen, in September, 1847, 

 selected the Brazilian species Bulimus melanostomus as type, 

 thus making Pachyotus a synonym of Auris Spix. See 



