1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 371 



ness, and often of a lighter color than the shell, appearing as a crimson 

 or otherwise colored '-collar," as one of my correspondents terms it. 

 Generally those species have it more conspicuously developed that have 

 a prominent crest and strong lamellae, but there are exceptions; thus 

 a species nndescribed, so far as I know, from Colorado (Table, No. 9), 

 showing the last-mentioned feature, has not a trace of a callus, or at least 

 my specimens have not. That there are differences in this respect in 

 one and the same species, V. curvidens, Gld., furnishes proof; most of my 

 specimens — I have them from various places in Ohio and several other 

 States — have a well developed and often very strong callosity, while a 

 ^w from Maine show no trace of it. This is constant in a number of 

 species with simple last whorl and straight peristome, as V. alpestris 

 Alder. That the callus is the homologue of the thickened lip in most 

 of our Helices, etc., there can be no doubt. 



Still another feature has to be considered in this connection. Behind 

 the crest named above — behind, if we suppose the plane of the aperture 

 to be in front — there is in some of the species a depression in the last 

 whorl. It is not very deep, well defined below (towards the base), grad- 

 ually disappearing above (towards the suture), occupying about the 

 half of the middle of the whorl. Although this may appear trilling, I 

 consider it a valuable feature in defining certain forms and species of 

 Vertigo as well shown in V. ovaia Say. (Fig. 7 at x.) 



The second of the main points is the dentition, a*proniinent feature 

 in this group, so striking, indeed, that it has probaoly had too much 

 importance given to it in many descriptions of species, while other char- 

 acters of equal value have been more or less neglected. And yet, never- 

 theless, it has not been studied with sufficient care, especially its occur- 

 rence and aspect as a whole, both in its grouping and as to the shape 

 of the separate lamelkc. This latter term I think to be better than 

 "teeth" or "denticles," for it defines more correctly their real shape 

 and typical value, as all of these, even the smallest, appear as lamellae 

 or folds, if examined with a magnifier of sufficient power, though in 

 some instances they are only quite rudimentary. So far as known they 

 vary in number and shape. Notwithstanding their variability in these 

 respects, there is exceeding persistency in the matter of position, not 

 only in the same species, but throughout the whole group of Vertigo ; 

 that is, if present at all. It appears, therefore, that the position of the 

 lamellae is of greater importance than their prominence. Whether one 

 of these be strongly developed, small, or entirely wanting, it has its own 

 particular or typically local place, and we know which are present and 

 which wanting. This point, therefore, should be stated in descriptions. 

 To appreciate this character requires a very critical examination, but 

 once understood it facilitates diagnosis very materially. (Compare figs. 

 1-4, 6, 9.) 



As already stated, the number and size of the lamella? vary in differ- 

 ent species. En general those with the crest near the aperture, with a 



