72 VERTIGO. 



reject the remainder as polynomial. In the present case, Gray 

 was in effect using subgenera, and not what is commonly 

 understood as polynomial terms; I have not found Gray's 

 publication of Isthmia in 1840, though he quotes that date 

 in his paper of 1847, where V. mtida (presumably = Pupa 

 edentula Drap.) is mentioned as the type. Isthmia has been 

 extensively used in Europe for the genus Truncatellwa Lowe. 



Al&a was proposed by Jeffreys for dextral Vertigines, but 

 later, in the British Conchology, he considered "this generic 

 addition to be quite useless and untenable." Dall has ex- 

 pressed a similar view; and I fully agree with these authori- 

 ties, although Boettger, Westerlund and most German authors 

 have used Al&a. Dexiogyra was proposed for the same group, 

 and is even less defensible. 



The value of Nearctula and Haplopupa remains to be as- 

 certained when the affinities of their type species are better 

 understood. They do not seem separable from the subgenus 

 Vertigo by sufficient characters, as at present known. 



Distribution of Vertigo. 



Vertigo is essentially a northern genus of humid stations 

 or regions. The group of Vertigo modest a is circumpolar, 

 numerous in races and individuals above the parallel of 60, 

 and extending south at increasing elevations, in the Canadian 

 and Transition zones, to about lat. 33 in Arizona, there only 

 in mountain-top colonies. In Europe it does not go so far 

 south, only to the Austrian Tyrol. 



Only 5 species of Vertigo have been reported from the 

 American tropical fauna (Mexico and the West Indies), 3 of 

 them being identical with northern species, the other 2 doubt- 

 fully distinct from the widely spread V. ovata. This identity, 

 together with the fact that they appear to be among the rarest 

 snails in those regions, surely indicates that Vertigo is a late 

 comer in the American tropics, if not, as I suspect, imported 

 by man. Species have been found as far south as about 

 18 N. Lat. 



In the Palsearctic fauna, Scandinavia and the eastern Alps 

 (Tyrol) have the greatest development of the genus. No 



