VERTIGO. 71 



In Europe, several diverse forms have given rise to smistral 

 species, but up to this time no sinistral species or specimens 

 have been reported from America or Japan. 



The shells of Vertigo are usually clean, but V. dalliana at 

 least occurs daubed with slime and dirt, like many 

 Gastrocoptinae. 



Key to the subgenera of Vertigo. 



a 1 . Angular lamella curving towards and connected with the 

 outer lip ; lamella and plicae well developed. 



Subgenus Ptychal&a, species no. 41. 



a 2 . Angular lamella, when present, standing free of the peris- 

 tome, not emerging to the edge. 



6 1 . Columellar lamella short, lamellar or toothlike, sub- 

 horizontal or inwardly ascending a little, sometimes 

 absent. Subgenus Vertigo. 



6 2 . Columellar lamella subvertical, spirally ascending 

 (pi. 5, fig. 18) ; upper palatal fold entering very 

 deeply, the lower shorter or wanting. 



Subgenus Vertilla, species nos. 81, 82. 

 b 3 . Columellar lamella subvertical, the upper palatal 

 fold shorter than the lower or wanting; no angular 

 lamella or basal fold in known species. 



Subgenus Vertttlaria, species no. 31. 

 & 4 . Columellar lamella curving down at its inner end 

 (pi. 13, figs. 2, 4) ; lower palatal fold entering very 

 deeply, much longer than the upper. 



Subgenus Angustula, species nos. 32, 33. 



Nomenclature. 



In his original publication of Isthmia, 1821, Gray refers to 

 only one species, identical with Vertigo pygnuea. On ac- 

 count of his somewhat irregular system of indicating the 

 groups of " Helix," Harris & Newton have ruled this paper 

 out as not binomial, stating that the name must date from 

 Gray, 1840. It may be observed that their ruling has not 

 been followed by any other author. All the names of a work 

 stand or fall together ; one cannot accept part as binomial and 



