SOUTH-WESTERN 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. holbroold) 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,ij; 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 Reptiles,” p. 205. 
t Ihering, H. von, “ Verhreitung der Heliciden.” 
f Pilsbry, H. A., “ Manual of Conchology,” Vol. IX., p. xxxii. 
§ Ihering, II. von, “ Verhreitung der Heliciden,” p. 442. 
