372 AMERICAN SPECIES OF VERTIGO. 



callosity and expanded margin, have also the most highly developed 

 folds; such as P. antivertigo Drap. (Europe), and ovata Say (N. Ain.)> 

 while in species with a simple configuration of these parts they are few 

 and small. To return to these relations: the number of lamella? may 

 vary from three, or perhaps less, up to ten or even twelve or fourteen. 

 (Sec figs. L-5, <i, 9.) Five of them are the most characteristic and typ- 

 ical, because the most constant and at the same time, in most cases, the 

 largest. For many years I regarded them as primaries; the others as 

 accessories. This was in Europe, when I had no species from North 

 America; but the latter so far as I know them, agree quite well with 

 those of the European continent, in general appearance and structure. 



The primary lamella' are as follows, designated with letters (see fig. 

 5) : one on the apertural wall or body whorl A ; one on the columella 

 T> : one at or near the base C : two in the outer margin or peristome 

 1) and E. A is the most constant in shape, being a well developed, 

 rather high lamella, steeply ascending at the ends, differing somewhat 

 in size, and in its being inclined to the inner or outer side in some species 

 (hence the name "curvidens"), as in the figure. 



B, if not closely looked at, appears to be simply a projecting tooth in 

 the columella while it is a true lamella, encircling the pillar in a direc- 

 tion nearly rectangular to the axis. It is a good plan in order to gain 

 an idea of its configuration and also of that of the others, to examine 

 and compare larger Pupce with well developed folds, e.g., P. dolium Drap., 

 and A torquillas, or our N". American P. armifera and P. contractu, in 

 which of course the lamella^ are partly of another type and shape. In 

 none of the Vertigo species I know is the columellar fold wanting. 



C is the least constant of all the primary folds, in fact in most in- 

 stances absent, and even in one and the same species it may be present, 

 or not, as in P. pygmcea Drap. And yet there are reasons for consider- 

 ing it not merely an accessory. It appears like a simple tooth, rather 

 variable in size, but really it is a lamella, although the shortest of the 

 primaries. In most instances its position is not exactly at the base, but 

 a little nearer the columella (see figs. 1-3, 5), so that many descriptions 

 say that there are two "teeth'' on the pillar, yet generally it is seen 

 through the transparent shell quite near the lowest part of the latter, 

 which is hardly a part of the columella. 



The two lamella- on the peristome are always easily recognizable as 

 such, but of very different dimensions. Where there is a callus, as de- 

 scribed above, they generally end in it, either beginning rather distant 

 from it in the " throat " or quite near, then sometimes simply appearing 

 to be a nodule upon it, especially when they are small. (Fig. 2.) Very 

 generally they are absolutely and relatively smaller in species having 

 no callosity and are isolated (Figs. 3, 4), while in others the callus con- 

 nects them. The lower of the two, D, is remarkably constant, and in 

 this regard, together with B, keeps the first rank, while the upper, E, 



