206 ORIGIN OF LIFE IN AMERICA 



tation of some anatomical facts. Dr. von Ihering supports 

 the opinions, upheld by almost all the prominent European 

 conchologists, that the west American shells, which so greatly 

 resemble the European Ariantas and Campylaeas, are really 

 genetically connected with the latter. He even contends that 

 no anatomical distinction worth mentioning exists between 

 some of the American Epiphragmophoras and the European 

 Arianta. Dr. Pilsbry, on the other hand, does not recognise 

 any very intimate anatomical relationship between the Euro- 

 pean and west American Helicidae, except in so far as he con- 

 siders both to be branches of an ancient south Asiatic stock. 

 As I shall explain later on, I concur with Dr. von Ihering, 

 Dr. Sandberger, Professor Oppenheim, Professor Boettger .and 

 Dr. Kobelt in the opinion that many of the Antillean and 

 west American forms are intimately related to extinct and 

 recent European Helicidae. The great resemblance of the 

 shells of Arianta and some of the Epiphragmophoras alone 

 seem to imply a near relationship between them. 



The genera Ashmunella, Sonorella and Oreohelix are quite 

 peculiar to south-western America, a large number of species 

 having been described by Dr. Pilsbry and Mr. Ferris * in a 

 series of articles contributed within the last few years to the 

 Proceedings of the Academy of Natural Sciences of Phila- 

 delphia. The same region contains many other distinct genera 

 of land mollusks. The Urocoptidae, a family of snails some- 

 what resembling the European Clausilia in shape, and having 

 their headquarters in the Antilles, are represented by two 

 genera, viz., Holospira and Berendtia, peculiar to south- 

 western North America. 



Of some interest is the occurrence in southern Mexico, in 

 lower California, and on the intervening islands,, of many 

 species of the large and ponderous genus Bulimulus. The 

 difficulty of satisfactory identification unfortunately is such 

 that there is little agreement among the various authorities as 

 to the limits or range of species, nor is the nomenclature of 

 these shells in a more satisfactory position. All the same 

 as I shall mention later on, we can gather some useful hints 

 from their distribution. 



* Pilsbry, H. A., and J. H. Ferris, " Mollusca of the South-Western 

 States." 



