1896.] NATURAL SCIENCES OF PHILADELPHIA. 417 



timate structure of these animal as related to the conditions in 

 which they live is the object of consideration. 



The Helices are of less importance in this discussion because we 

 do not know what species may be found to inhabit the Galapagos on 

 thorough search. But we may, in passing, note that the species 

 have certain characteristics which are almost exclusively found in 

 members of insular founas, of which the most remarkable are the 

 parallel spiral lamellae running inward from the aperture. They 

 are obviously protective and their presence would suggest a peculiar 

 enemy, entering the aperture to devour the inhabitant of the shell, 

 as prevalent in island faunas. 



If we examine PfeifFer's list of species belonging to the section of 

 Patula called Endodonta, to which these Helices were referred by 

 him, we shall find that of those with basal lamellae all are insular 

 species, the largest body of land to which any species is referred be- 

 ing Tasmania. Of the eighteen forms with parietal lamellae all are 

 insular on tropical islands from New Caledonia to Hawaii. Of 

 those with both parietal and basal lamellae, omitting those described 

 from St. Helena, the entire thirty-three species are insular and from 

 mountainous tropical islands, most of which are known to be vol- 

 canic. 



Of the other land shells the singular P(?j;a or Tomigerus perexilis 

 appears to be a local development, but there are two ordinary 

 Pupas one of which is very similar in its general features and type 

 of lamellation to the Noronha and Galapagos species, a likeness 

 already noted by Smith. The Succiueas again, over and above the 

 general similarity of the species everywhere, exhibit certain pecu- 

 liarities, which appear to be associated with an insular habitat. The 

 Siiccinea brevior of the Galapagos can hardly be discriminated from 

 S. hekmce from St. Helena. S. Bettii is parallel with S. pida, and 

 S. Wolfi. with Bensoniana. In endeavoring to find, in our large 

 collection of domestic and foreign Succineas, some species with 

 sculptured surface to compare with S. corbis, the only forms of the 

 kind which the National Museum afforded wex'e insular, from Samoa, 

 Martinique, St. Helena, etc. Doubtless the peculiar vermicular or 

 dichotomous impressed lines which these species show are due to 

 causes similar to those already described which modify the surface 

 sculpture in Bullmulus. Not all them show it, but those which do 

 show it are, so far as I have yet observed, either insular or subjected 

 to locally arid conditions. Those species in which this sort of sculpt- 

 ure has become habitual are all insular and tropical. 



