370 AMERICAN SPECIES OF VERTIGO. 



to the soft parts my material lias not been sufficient nor ray study pur- 

 sued far enough to warrant present consideration. 



I shall not here present any systematic description of species — old 

 or new — nor enter into critical discussions about synonomy, etc., except 

 in a few cases necessary to my purpose, leaving such questions for later 

 publication. The present will be only a general statement of a part of 

 the characteristics of the Vertigo group as obtained by comparing North 

 American and European species and forms, and the conclusions arising 

 therefrom. These latter necessarily lead to the creation of a new sub- 

 genus of Pupa in order to properly segregate and place a few species, 

 which in our sense are essentially different from the Vertigos. It is not 

 necessary for our purpose to describe all parts and features of the Ver- 

 tigo shell. Its size, shape, striation, coloration, whether umbilicated 

 (widely or narrowly perforated) or not; the number and shape of the 

 whorls, the relative size of the latter in respect to the ratio of their 

 growth, the sutural character, etc., all of these we will put aside, and di- 

 rect our attention to two principal points, closely connected, namely, the 

 configuration of the last whorl near the aperture and of the latter itself, 

 and its denticles. This last term is used for convenience, and has 

 nothing to do with the odontophore of the animal, but refers only to the 

 lamella? of the aperture. The latter is of nearly similar shape in all the 

 Vertigos ; more or less half-oval or rounded, except at one point a little 

 above the middle of the outer wall, or peristome, where there is, in some 

 species, an indentation dividing the outer margin in two parts or curves, 

 the upper of which is the smaller. (See Plate XLII, Figs. 1, 5, 6, 9, 11.) 

 There are gradual differences in this feature, and many species show only 

 a trace of that indentation, or slight flattening of the outer wall (Figs. 4, 

 9). Occasionally this point projects beyond the plane of the margin, 

 as a rather prominent angle in some species, e. g., Y. ovata Say, or as a 

 slightly rounded elevation in others; a few have scarcely a trace of it. 

 It is seen when looking vertically at the plane of the aperture. This is 

 a feature by no means peculiar to Vertigo; in many gastropod shells 

 it is more or less perceptible, especially in most of our laud and fresh 

 water "snails," although in few so marked as in V. a ntirertigOjDrap., ami 

 some others, among which are P. milium, Gld., and P. venctzii Charp. 

 At a little distance from the outer margin and parallel to it and to the 

 lines of growth there is an elevation, iu form of a prominent crest, sepa- 

 rated from the margin by a more or less deep groove or constriction. (See 

 Fig. 7 x .) But there are again great differences in the aspect of this ; in 

 many species the crest is scarcely perceptible and the whorl continues 

 with little change of form to the very margin, which then is geuerally 

 not at all or but slightly expanded (Fig. 3), while it is considerably so iu 

 those species showing the above-named configuration iu a marked degree. 

 (Fig- 7.) 



Inside, corresponding to the crest on the outside, many species show 

 a callosity e-xtend-w-ig from the base to the suture, very variable iu thick- 



