378 AMERICAN SPECIES OF VERTIGO. 



well formed, high and thin and ending abruptly, when of the primary 

 D to be connected with it there was not yet a trace to be seen. 



The second distinguishing feature is the conformation of the last 

 whorl ; it is considerably narrowed toward the aperture, so that the 

 whole shell diminishes at both extremities (hence the name of an- 

 gustior Jeffr.). A deep impression near the base towards the aperture, 

 corresponding to the upper primary, going through the crest to the 

 very margin, adds to the peculiar character of the shell in both species. 



Another highly important point is the shape and oblique direction of 

 the columellar tooth (figs. 10, 11), again simulating Clausilia and not 

 encircling the pillar as in most of the other groups of Pupa. I be- 

 lieve that if the size of our species was ten times what it is, their rela- 

 tion to Clausilia would have been remarked ere this. 



To these characteristics may be added another; the lower primary 

 lamella D in the peristome is much smaller than the upper, E, whether 

 isolated or united with the gular. In venetzii it is very small, while 

 in all Vertigos it is at least as large as E and very often a trifle larger, 

 and is present in species having no upper E, or only a trace of it. 



To briefly recapitulate the main distinguishing features of our group, 

 they are, (1) the narrowed ultimate whorl, with deep constriction; ^2) 

 the long gular lamella, connected with one of the outer primary teeth; 

 (3) the position of the columellar lamella along the pillar; (4) the small 

 lamella D on the peristome. These characteristics separate our species 

 widely from Vertigo, and require for them a distinct group; they must 

 be considered as constituting a subgenus, as valid and well char- 

 acterized as any other. I suggest for it the name of A?igustula, re- 

 ferring to the narrower whorl, and at the same time recalling Jeffrey's 

 name angustior for P. venetzii Charpeutier. That one of the two 

 is dextral, the other sinistral, is no reason against uniting them in 

 one group. It is not without interest to note the fact that one in- 

 habits the Old World and the other the New, in which there are found 

 so few typically sinistral land-pulmonates. One is nearly like the mirror 

 image of the other, yet there are a number of differences between them 

 which may be presented as follows : 



P. milium Gld. 



dextral. 

 finely striated. 



gular lamella united with the lower 

 primary D. 



■ basal fold C long, lamella-like. 



■ a small but distinct lamellaouthe per- 



istome above E. 

 without the nodule. 



P. vertigo Charp. 



— sinistral. 



— strongly striated. 



— gular lamella united with the upper 



primary E. 



— the basal C short, nodule-like. 



— without the lamella. 



— a small nodule on body-whorl at the 



upper angle connected with the lam- 

 ellar accessory. 



