SOUTH-WESTEEN TOADS 205 



ences. The spade-foot toads (Scaphiopus), as they have been 

 called, have their headquarters in Mexico and the south- 

 western States, whence they have spread northward along the 

 Pacific coast and eastward to the Atlantic States.* One 

 species, the hermit spade-foot (S. holbrooki) is worthy of 

 special note, owing to its occurrence on Martha's Vineyard 

 Island, in view of the remark I previously made (p. 183) 

 that this and other north-eastern islands are the remnants 

 of an ancient land mass formerly connected by land with the 

 mid -Atlantic land bridge. 



The faunistic relationship between Europe and south- 

 western North America deserves an ample discussion, being 

 one of the most important and noteworthy features of the 

 American fauna. Besides the points already referred to 

 there are a few others which throw light on the nature and 

 origin of this relationship. 



I do not intend to dwell on the merits of the various classi- 

 fications which have been adopted for the land mollusks. Even 

 if we base our system upon purely anatomical grounds, dif- 

 ferent points of view may sometimes give rise to considerable 

 differences in classification. Thus Dr. von Ihering f contends 

 that the family Helicidae, as far as North America is con- 

 cerned, is entirely confined to the western States. Dr. 

 Pilsbry,J on the other hand, in including Polygyra among 

 the Helicidae, naturally records for that family a very 

 different range. 



Both authors agree in attaching great importance to the 

 molluscan fauna of the western and south-western States, 

 and both are inclined to attribute its origin to immigration 

 from Asia. That Dr. Pilsbry supposes the mollusks to have 

 wandered across an old Bering Strait land bridge, while Dr. 

 von Ihering argues in favour of a much more southern 

 Oligocene land connection between eastern Asia and Cali- 

 fornia, is not perhaps of such fundamental importance. The 

 general agreement is all the more remarkable, as both 

 authors have formed radically different views on the interpre- 



* Gadow, H., "Mexican Amphibians and Keptiles," p. 205. 

 t Ihering, H. von, " Yerbreitung der Heliciden." 

 J Pilsbry, H. A., " Manual of Conchology," Yol. IX., p. xxxii. 

 Ihering, H. von, " Yerbreitung der Heliciden," p. 442. 



